Durham, UK $-$ 29 July $\rightarrow$ 02 August 2019
- Overviewing Munshi+ (2019) and Applebaum+ (in prep)
- Focusing on the dependence on SF prescription -- metal cooling vs H$_2$ (see Benincasa+ 2016)
- DM resolution of 6000 M$_\odot$; SF; MBH formation & feedback; H$_2$ formation; SIDM
- With MC runs, SMHM relation is much shallower than the H$_2$ runs. The H$_2$ runs have much fewer UFDs than the MC runs because of reionization quenching
- DC Justice League simulations: Following dwarfs around a MW-like halo. Still running.
- No dependence on SF prescription, unlike the earlier simulations, which focused on a collapsing sheet (isolated)
- Differences in the MDF between prescriptions, but they don't include Pop III stars even though they look at EMP stars
- Reviewing Rey+ (2019) & (in prep), Agertz+ (2019). Inspecting the dependency on reionization histories on dwarfs
- Looking at why dwarfs don't have surface brightnesses below 31 mag/arcsec$^2$
- EDGE simulations: 1000 M$_\odot$ DM particles, 3pc resolution, IC genetic modifications to vary halo mass accretion (used to explore the effects of reionization -- early vs late growth)
- Early growth in UFDs at a fixed mergers
$\rightarrow$ Higher stellar masses (by an order of magnitude) - The lower stellar mass UFDs have the same size as the more massive ones -> lower surface brightness (25
$\rightarrow$ 32 mag/arcsec$^2$) - This can explain the scatter in the magnitude vs. half-light radius relation
- The very low mass UFDs have stellar masses around
$10^4$ M$_\odot$ and grow through dry mergers (no SF) after reionization
- Exploring the dwarfs outside the MW and M31, using the APOSTLE simulations
- Penarrubia & Fattahi (2016)
- 12 LG-like volumes
$-$ separation between MW & M31, relative radial & tangential velocities, MW & M31 masses, Hubble flow
- Mass within 3 Mpc is 3-4 times the MW+M31
- There exists a tight correlation between total mass and dwarf galaxy numbers (about some stellar mass)
- Predict missing ~50 dwarf galaxies (
$M_\star > 10^5$ ) in the LG
(Belokurov) Antila 2, the hidden giant
- (Di Cintio+ 2014; Bullock & MBK 2017) Inner DM slope vs baryon fraction relation of galaxies
$-$ caused by feedback? - Found a new massive satellite, using RR Lyrae stars to determine a distance of >70 kpc. Distance is 130 kpc where they used the BHB (from DECCam) as a standard candle
- 3kpc half-light radius,
$M_V = -9$ ,$\mu = 32$ mag/arcsec$^2$ - Metal-poor: stars mainly between [Fe/H] =
$-2.5 \rightarrow -0.5$ . Typical classical dwarf MDF, peaking at$-1.5$ . - Why are these diffuse galaxies so "fluffy"? Efficient feedback is one explanation.
- (Errani & Penarrubia 2019) What about tidal stripping? Galaxies in core halos experience more stripping, losing a lot of mass, creating fluffy galaxies.
- Using FIRE-2 simulations (see Lazar+ 2019)
- Found a universal "core-Einasto" profile from tiny dwarfs to MW
- Found a mass estimator for transverse velocity dispersions in spheroidal galaxies
- Inner DM slope is cored in bright dwarfs (cored in DM-only runs)
- Agreement with previous work: "sweet spot" for core formation (
$M_\star \sim 0.005 M_{\rm halo} \sim 10^9 M_\odot$ ) - Changes with previous work: More diversity and scatter in core properties. Cuspy profiles in small galaxies (
$M_\star < 10^6 M_\odot$ )
- Agreement with previous work: "sweet spot" for core formation (
- Dwarfs with
$M_\star < 10^6 M_\odot$ are good places to test DM, e.g. SIDM creates cores. - However, these dwarfs are dispersion dominated, so it's hard to determine a mass profile. One can measure the mass at a particular radius from LOS velocities
- Also can use tangential velocity dispersion (Lazar & Bullock 2019). Mass is independent of anisotropy at radius where log-slope tracer is -2
-
$M(r_{-2})$ is related to the LOS velocities, where$r_{-2}$ is fixed (see Lazar & Bullock 2019)
- (Graus+ 2018; Garrison-Kimmel+ 2018; Kelley+ 2018) Subhalo disruption in MW-like halos, shown in FIRE-2 simulations, where there is tidal disruption from interactions with the disk potential
- To test the reionization quenching of dwarfs, one can look at the cutoff mass (or velocity dispersion. A cutoff velocity between 10-15 km/s works best.
- (Ricotti+ 2016) Extremely small dwarfs can form in externally enriched halos
- With strong lensing, one can measure DM profiles from the perturbations between the multiple images
- Requires a ~mas source. Tradtionally limited to radio loud jets (very rare). But more recently has been exteneded to galaxy-scale lenses and now narrow line region (this talk)
- Full-forward modeling: getting quantitative analysis of the DM properties (Gilman+ 2019)
- Can get a constraint on smallest DM halo mass (if WDM) by measuring the number of lenses in the LOS
- Simulation (20 Mpc) with
$10^4 M_\odot$ gas particles, looking for dark halos (no gas, no stars) - Have calculated the HI column density profiles for different halo masses (detectable with 21cm?)
- Compared with observations (Benitez-Llambay+ 2017, in prep)
- (Sykes+ 2019) Dark galaxies will glow in H$\alpha$ from recombination
- Calculated in spherical symmetry (code on github). Most of the H$\alpha$ emissivity comes from mid-radii (~kpc) because at high density, most the gas is neutral.
- Strong peak at the ionization front (from the background)
- The emissivity peak depends on the DM profile
- Using both H$\alpha$ and 21cm, one can break degeneracies in halo mass
- Helium recombination is also important (but 3-5x dimmer) and can be used to measure primordial helium abundance
- Impracticable to find around MW but surveying comparable volume, it is much easier around other galaxies (because of sky coverage of a galaxy)
- Using OLAS to survey kinematic properties of 21 lensed galaxies at z=1.25-2.29 between
$\log M_\star = 8-10$ - (Hirtenstein+ 2019) Comparing observations with FIRE-2 simulations. The observed galaxies sample the high end of the sSFR distribution (over both 10 and 100 Myr timescales)
- Cusp
$\rightarrow$ higher$f_{\rm DM}$ $\rightarrow$ lower$f_\star$ - Core
$\rightarrow$ lower$f_{\rm DM}$ $\rightarrow$ higher$f_\star$
- Reviewing dark matter heating from SN feedback (Read+ 2016)
- (Read+ 2018abc) Less star formation
$\rightarrow$ more cusp. Looking at WLM, Fornax, and Draco, comparing the SFH and density profile - If the SF was truncated early on, the DM profile is cusped
- DM central densities are anti-correlated with
$M_\star / M_{200}$ - Cored systems are much easily disrupted during infall
- (Genina+ 2019) Using the APOSTLE simulations to look at the metal-rich and metal-poor populations that are spatially distinct
- Matches the observed mass-metallicity relation In isolated dwarfs, galaxies dominated by merger growth are more segregated
- Satellite dwarfs are influenced by mergers, interactions with filaments, and at pericenter.
- At pericenter, SF burst induded, producing an MDF that's peaked
- Fornax-mass systems likely formed their metal-rich stars during pericenter
- However, it's probably not possible to distinguish whether the metal-rich population formed through mergers or at pericenter because the MDFs are too similar
- (Genina+ 2018) Viewing angle of dwarfs can change the effective radius and mass estimate
- (Kim+ 2018) Using completeness corrections, there is no missing satellite problem
- For each dwarf observed with brightness
$M_V$ and dispersion$\sigma_v$ , constructed a CDF of satellites w.r.t. radius - If compared to SIDM, the cross-section can't be bigger than ~0.3 cm$^2$/g
- For cored profiles, a transition from cusps to cores needs to happen at
$10^{10} M_\odot$ - CDM with baryons does a decent job explaining satellite kinematics (but too many satellites with disk stripping)
- Using ETHOS model to explore core-cusp variations, in addition to SF, hydro, and SN feedback
- Power spectrum is cutoff below
$\sim 10^{10} M_\odot$ with a bump (dark acoustic oscillations) at$\sim 10^8 M_\odot$ - (Lovell+ 2019) Get a SF enhancement in halos with log M/M$_\odot$ = 8-10
- Halos below
$10^{10} M_\odot$ are delayed up to 200 Myr compared to CDM
- Motivation: small-scale theoretical challenges to LCDM; no CDM particle found yet; 3.5 keV line
- To test the validity of WDM models (thermal relic, in particular), need satellite galaxy luminosity function
- Use EPS formalism that is calibrated against simulations for "missing subhalos" (when halo finders can't find them).
- Inspecting halos between
$0.5-2.0 \times 10^{12} M_\odot$ - Rules out WDM models with
$m_{\rm th} < 2.2$ keV after comparing with observations - Without correcting for missing subhalos, the constraints are much higher (< 3.0-3.5 keV)
(Kallivayalil) The Missing Satellites of the Magellanic Clouds: Testing LCDM Predictions on Small Scales
- UFDs:
$\log M_\star/M_\odot = 3-4$ ;$M_{\rm halo} \sim 10^8 M_\odot$ - How many Magellanic satellites does LCDM predict?
- For group infall, see Sales+ (2013), Wetzel (2015), Deason+ (2015)
- 2-12 UFDs with
$M_\star > 10^4 M_\odot$ (Dooley+ 2017)
- (Sales+ 2017; Kallivayalil+ 2018) Using a (zoom-in) cosmological simulation to explore a MW-like system with an infalling LMC-like system
- Discovered 8 new UFDs with Gaia DR2 (Hor1, Car2, Car3, Hya1, Phx2, Dra2, Hya2, Ret2)
- Carina and Fornax are likely associated with the LMC
- Using Gaia DR2 to search for satellites of LMC+SMC and orbital modeling of satellites during infall (Erkal & Belokurov 2019; Patel+ 2019)
- (Jahn+ 2019) FIRE-2 simulations that have consistent satellite numbers for (isolated) LMC analogs. Also see Munshi+ (2019)
- (Geha+ 2017) Satellite mass functions for 100 MW-mass analogs
- But it is much harder to search for satellites of smaller galaxies (<
$10^{11} M_\odot$ ) - M33: Isolated LMC counterpart
$M_\star = 3.2 \times 10^9 M_\odot \rightarrow M_{\rm halo} \sim 10^{11} M_\odot$ - 200 kpc from M31
- ~10% of M31's mass
- Morphology shows hints of previous interaction (50-100 kpc about 3 Gyr ago)
- (Patel+ 2017; van der Marel+ 2019) Orbital modeling of M31+M33. Ran 10k integrations, but found <1% of orbits reached 55-100 kpc within the last 3 Gyr
- First infall?
$\rightarrow$ satellites should have survived until today - If not, more likely last interaction with Gaia DR2: ~6 Gyr ago within ~100 kpc. Less satellites than the first infall case
- First infall?
- (Dooley+ 2017; Patel+ 2018) Prediction of
$8 \pm 4$ satellites with$M_\star \ge 10^4 M_\odot$
- (El Badry+ 2016) In low-mass galaxies, feedback drives outflows, bursty SF, and dispersion-dominated galaxies
- (El Badry+ 2018) Inspecting different LOS (simulated) spectra and rotation curves for different types of galaxies -- irregular, intermediate, and rotating disk, where the latter is quantified by the kurtosis of the HI line.
- FIRE simulations produce overly dispersion dominated galaxies at
$M_\star \sim 10^9 M_\odot$ . - Non-cosmo simulations match observations better. They're still figuring out why.
- Gas accreting at late times typically has more angular momentum than earlier.
- Why do we care? AGN feedback in dwarfs; IMBHs in dwarfs
$\rightarrow$ SMBH seeding, LISA, fundamental physics about fueling - No current direct evidence for BHs between 60 and
$10^4 M_\odot$ . Need to catch them in the act of accretion - (Groves+ 2008; Cann+ 2019) Complication: low-metallicity galaxies with AGN (especially low-mass ones) look like SF galaxies
- Determining better ID methods with JWST in IR: Use high-ionization lines -- SiXI and MgIV lines for example -- insensitive to extinction and XRBs
$\rightarrow$ LLAGN? - (Cann+ 2019, submitted) Strong ionization line in J1056+????, constraining [Fe/H] (?) between 6-48%
- Covering recent paper on arXiv (Manzano; 1905.9287)
- AGN are present in dwarf galaxies (e.g. Reines+ 2013), and their feedback could be important (e.g. Koudmani+ 2019)
- Chose 50 dwarf galaxies: 29 AGN, 21 SF (based on BPT diagram)
- Inspecting (H$\beta$, H$\alpha$, [OIII], [NII]) line profiles to determine whether the outflow is originating from AGN or SF.
- The galaxies in the AGN portion of the BPT diagram most likely have their outflows driven by AGN
- But does this gas escape from the galaxy? Yes.
- SF-driven outflow galaxies are bluer than the AGN-driven ones
- Describing latest paper (Koudmani+ 2019) exploring AGN feedback in dwarfs, especially the maximal impact.
- Simulations with AGN produce higher temperatures and stronger outflows but doesn't affect overall SFR. Central SFR is decrased, though.
- There's no cosmological inflows because these simulations are isolated.
- Comparing simulations with MANGA survey. Stellar motions unaffected by feedback. SN outflows are too weak to affect kinematics, but AGN is.
- Dense (more massive) WDs are neutron-rich because beta decay cannot happen because all of the electron states are occupied. Neutrons are created through electron capture.
- Less massive (less dense) WDs produce less neutrons
$\rightarrow$ more stable isotopes, like Ni - Inspecting 5 dwarfs, focusing on Sculptor in the talk (Kirby+ 2019)
- [Mg/Fe], Si, Ca, Cr, Co vs [Fe/H] decline at higher values, as usual. But [Ni/Fe] is flat. Using these data to determine what fraction came from CCSNe vs. SNIa w.r.t. [Fe/H]. Increasing from 0 to 1 between [Fe/H] = -2 to -1.
- Ancient dwarfs are iron enriched through sub-Chandrasekhar mass SNIa
- However dwarfs with extended SFHs have higher [Ni/Fe] and probably have Chandrasekhar mass SNIa
- Measuring masses of all known Andromeda dwarfs (And XIX, XXI, XXV, for example). Increased Andromeda low-mass dwarf membership by three.
- And XIX: Is this tidally stripped? UFD analog? Low mass?
$\mu \sim 30$ mag/arcsec$^2$ ($r_{\rm eff}$ = 3 kpc). Very similar to Antila 2. - Including new data, there is lower velocity dispersion on one side (10 vs 2 km/s). Possible substructure?
- Antila 2: Feedback and tidal stripping during a very close pericenter passage (~25 kpc) probably induce the galaxy to puff up
- What about And XIX? Following it up with dynamical modeling now.
- And XXI: Low mass, low density (
$\sim 10^7 M_\odot$ kpc$^{-3}$) outlier. Can this be done with feedback? (Read+ in prep) It is consistent with a cored profile. Needs to form stars for nearly a Hubble time to explain low density. - But there hasn't been any SF for 3-5 Gyr (Martin+ 2017)
- And XXV: still working on stellar membership. Low-mass but not extreme
- Using the Romulus25(C) simulations to study LSB (UDG) galaxies, where there are ~500 UDGs in Romulus25 and C
- For a stellar mass of
$10^8 M_\odot$ most (80%) galaxies are UDGs in clusters, whereas only ~25% of isolated ones are UDGs$\rightarrow$ 8.5 x 10$^{-3}$ Mpc$^{-3}$ number density - In isolated UDGs, halo masses are spread between
$10^{10-11} M_\odot$ , and their sSFRs and HI mass are similar to isolated dwarfs - Most simulated UDGs grow in size in the past 8 Gyr (more massive galaxies grow more), where isolated dwarf sizes are stable
- On average, UDGs have lower sSFR within 500 pc at later times
- High halo spin doesn't cause UDG formation
- Overview of DM content of dwarfs and their multiple stellar populations
- (Sohn+ 2017) Use internal proper motions with HST to determine orbital properties. Sculptor requires ~22 $\mu$as/year!
- (Massari+ 2018, 2019) Use Gaia for Sculptor (
$\sigma_{\rm R,T} = 11.5, 8.5$ km/s) and Draco ($\sigma_{\rm R,T} = 11.0, 9.9$ km/s) - Need transverse velocity dispersion down to ~1 km/s to determine the central DM slope
- Sagattarius: Found a "cold spot" in the core's velocity data (Pace & Strigari 2019). Velocities dispersions (in all directions) are ~15 km/s with some(?) deficit in the inner 100-200 pc.
- (Stringer+ 2019; Ferguson+ in prep) Use RR Lyrae from DES for Scu, For, and Sag
- (Wang+ 2018) Search for stream from Fornax. Need a sensivitity of ~32 mag/arcsec$^2$. Found nothing.
- Omega Cen: Emits
$\gamma$ -rays, along with 20 other GCs. Consistent with having DM (Brown+ 2019; Reynosa-Cordova+ 2019). Lower central density (decreases) than models without DM. Best fit DM spectrum: 31 GeV.
- Particle physics point of view
- DM constraints depend on accurate J-factors (i.e. LOS integrated of
$\rho_{\rm DM}^2$ ). See Simon+ (2019) review for uncertainities - Important assumptions: equilibrium, spherical, non-rotating, no binaries. How does this affect DM annihilation (decay) constraints? (Spencer+ 2018)
- (Gaia Challenge) Use simulated data (Plummer light profile, Cusped DM profile, no anisotropy) to try to fit their model (Spencer+ 2018) to see how binaries affect the constraints
- Including binaries increases the J-factor but it's within the error bars
- Future work: More tracers, injecting binaries in certain regions, more flexible DM profile, include other systematics
- About a decade ago, simulations were just beginning to sample 100s of MW-like galaxies, building up statistics. But we only have one Milky Way! How do we reconcile this?
- Came up with the SAGA survey: To observe 100 MWs, need a volume of radius 30 Mpc
- Phase I: (Geha+ 2017) Found 8 complete hosts, 27 satellites, 2 of 21 quenched (compared to 3 of 5 in the MW)
- Phase II: (Mao+ in prep) Found 21 complete hosts with deep imaging, 77 satellites, 8 of 63 quenched
- More in progress! 49 hosts, 157 satellites, 12/119 quenched
- Spectra are high S/N and able to detect absorption and emission lines, i.e. SF vs quenched LSB galaxies.
- Only 3 LG-like objects within 30 Mpc
- Radial distribution of satellites is more consistent with an NFW profile with
$c = 10$ - Full redshift catalog at [http://sagasurvey.org]
- Using proper motions to determine velocity dispersions. Combining HST and Gaia DR1+DR2 data for the two epochs
- ID'ed 45 members of Draco with radial (11.0 km/s), LOS (9.0 km/s), and transverse (9.9 km/s) velocity dispersions. Used a dynamical model, varying
$\beta$ and$V_{\rm max}$ . - Draco density profile is consistent with a cusped profile
- (Hsyu+ 2017) New survey to identify the most metal-poor galaxies based on SDSS. Found ~100 new systems. Half have 12+log(O/H) < 0.1
$Z_\odot$ . - Found one of the most metal-poor systems, named the "the little cub" galaxy
- Now they are trying to measure the primordial $^4$He abundance
- Stellar feedback is important in small galaxies, but how much? Can observations constrain the findings of simulations (i.e. outflows)?
- Need to study: Hot (X-ray, fast low-density metal-rich winds), warm (UV/opt, slower but more mass), cold (ALMA)
- Using STARBIRDS program, 20 gas-rich SF galaxies
$M_\star = 10^7 - 10^{9.3} M_\odot$ - How far do the winds reach? CGM? Neutral winds in UGC6456 goes out to 10 scale heights of the disk, which is much smaller than simulators' definition of the CGM (0.1
$r_{\rm vir}$ ) - What is the mass loading factor? When was the wind launched? Use the CMD to calculate SFR ~ 0.03
$M_\odot$ /yr for the last 400 Myr. - (McQuinn+ submitted) Mass loading factor are between 1 and 7. But if scaled to
$V_circ$ , they find that$\eta = \dot{M}/SFR \propto V_{\rm circ}^{-0.96}$ .But simulations find much higher total mass loading values (up to an order of magnitude).
(James) Exploring Star-formation & Inhomogeneity in Pristine Environments: IFU Studies of Metal Poor Dwarf Galaxies
- Metallicity gradients
- Negative: inside-out growth, flattening with time
- Positive: tidal mixing, interacting systems (low-z); infall of pristine gas (high-z), SNe blowout + fallback, metal mixing, self pollution?
- There are small chemical variations in dwarf galaxies, down to 1 pc.
- (Koposov+ 2015, 2017) But this talk will be focusing on blue diffuse dwarfs.
- Used SDSS to find ~120 new LSB systems, where 25% are metal-poor (<0.1$Z_\odot$)
- Random regions of active SF in diffuse continuum
$\rightarrow$ akin to high-z systems - How is SF triggered in these systems? Turbulence? Feedback? External pressure?
- (James+ in prep) JKB18. No apparent outflows.
- Most of the gas is photo-ionized, but there are gradients that aren't aligned with SF regions, suggesting that it's occurring from shocks and turbulent.
- ~0.5 dex metallicity variations (O3N2)
- Only small scale variations, considering a random distribution of SF -- ages, gas velocities
- No metallicity correlation between regions in age or SFR. No evidence of self pollution. Simulations don't tell much about this.
- (Hernandez+ in prep) No variations in metallicity between the neutral and ionized phases
(Kumari) Chemical properties of Blue Compact Dwarf Galaxies: Local Analogues of High Redshift Galaxies
- Looking at the chemical inhomogeneous in BCDs at the pc-scale, possible ionization mechanisms, and stellar properties (age, SFR) of the ionizing population
- (Kumari+ 2018) NGC 4670. Spatially resolved HII regions in H$\alpha$ but not [OIII].
- Found an anti-correlation between [N/O] and [O/H] in some galaxies, opposite of what's expected (see Lopez-Sanchez+ 2010). Similar to green pea galaxies?
- Possible causes of the anti-correlation: Nitrogen enhrichment, SF efficiency, simulataneous inflow/outflow, SN triggering winds
- (Kumari+ 2017) NGC 4449. Metallicity gradient in radius (metal-poor center). Evidence of enrichment from winds?
- Studying the impact of reionization on dwarfs
$\leftrightarrow$ the impact of dwarfs on reionization - Constraint reionization by measuring
$\rho_{\rm UV}$ (with the UV LF) and$\xi_{\rm ion}$ (ionizing efficiency) - Lyman continuum is very difficult to detect and measure. Until ~2015, there were only about five detections. But there's been an explosion of detections in the past few years! (e.g. Siana+, Vanzella+, Shapley+, Rotkowski+, Steidel+)
- Discoveries started to happen because people started to look at the right galaxies. High-z analogs of green pea galaxies.
- Compact and strong SF galaxies. Outliers in the z=0 SFR-Mstar relation but consistent with the z=2 one
- Extreme emission lines in [OIII]/[OII] (O32), suggests high UV escape fractions
- Ly$\alpha$ peak separation indicates a low HI column density. Leaking ionizing photons?
- Need both Ly$\alpha$ and O32 to select LyC galaxies
- (Izotov+ 2016ab, 2018) Observed 10 galaxies, found 10 LyC detections!
$f_{\rm esc}$ = 2-70%
- (Scarlata+ in prep) Finding unusually low H$\alpha$/H$\beta$ ratios compared to the usual 2.86 in HII regions.
- Using SDSS, found that there's a large tail in low Balmer decrement for galaxies with high O32.
- What's going on? Possible explanation: gas optical depth to Balmer photons is not negligible, i.e. there is a substantial population of HI in the n=2 level.
- Then Balmer photons would be scattering around the absorbing medium
- This implies a dependence on viewing angle, creating a scatter in the relation
- Also can use H$\alpha$/H$\beta$ vs H$\gamma$/H$\beta$ to determine whether dust is important
- Important to quantify Balmer self-absorption and dust to determine intrinsic properties of the galaxies, especially when constraining the sources of reionization
- (Davies+ 2018) New constraints on reionization (z~7)
- Galaxies can provide enough ionizing photons if the LF steeply rises until
$M_{\rm UV} \sim -13$ - Comparing physical properties of z~3 galaxies and z>6 ones
- sSFRs are higher by ~5x
- Strong nebular emission lines (1000-3000A for [OIII]), 10x stronger in CIII], strong CIV powered by low-Z massive stars (or HMXBs?)
(Siana) Dwarf Galaxies in the Early Universe: Burstiness, Metals, Dust, and Ionizing Photon Production
- Want to compare observations with simulations, especially the bursty nature of low-mass galaxies (e.g. FIRE-2 simulations). If they are bursty, what are the consequences of the burstiness?
- (Emami+ 2018) Characterizing the burstiness, looking at the large scatter in SFR-$M_\star$ relation.
- Do the low-mass galaxies have larger scatter? But this doesn't really explain it because gas fractions can be different
- Use a combination of exponential rise/fall of SF events. H$\alpha$ traces new stars (3-5 Myr), and UV traces young stars (~20-100 Myr)
- Observations of
$M_\star < 10^8 M_\odot$ suggests burstiness ($\tau < 30$ Myr)
- (Emami+ in prep) Ionizing photons:
$\xi_{\rm ion}$ = (ionizing photon rate) /$L_{\rm UV}$ = C L${\rm H\alpha}$ / L${\rm UV}$- Above
$M_\star = 10^8 M_\odot$ ,$\xi_{\rm ion}$ is nearly constant, but there are more scatter in lower mass galaxies. Burstiness? - Q1: What is the "typical" galaxy? Median or average of
$\log(\xi_{\rm ion})$ - Q2: What is the consversion from LFs to ionizing photon rate per volume? Add up all ionizing photons in a volume-weighted manner and then take the average of the log.
- 0.3-0.5 dex evolution from z=0 to z=2 in
$\xi_{\rm ion}$
- Above
- (Gburek+ 2019) z=2.6 magnified (
$\mu = 8$ ) galaxy. Metallicity of 25% solar.$M_\star = 10^{8.1} M_\odot$ . SMC stellar mass but same metallicity. High compared to FIRE-2 mass-metallicity relation. Is there a large variability in metallicity during the bursts? Maybe
- Solo survey: Nearby dwarfs within 3 Mpc and isolated (>300 kpc from MW & M31) with CFHT and Magellan
- (Higgs+ in prep) Can resolve some stars (plus integrated light) in the dwarfs, measuring extended radial profiles and Sersic profiles
- Measuring the position angel, scale radius, ellipicity, and distance of these galaxies.
- Working on following Qs: How does shape/size vary with distance? (tidal effects). Trends with SFHs? Reshaping from internal processes. Comparison to Fornax and M101 etc? External environmental effects.
- SHIELD population: 5-12 Mpc away,
$M_{\rm HI}$ ~$M_\star$ 3-50 x 10$^6 M_\odot$ - What about UFDs? Leo T: most distant UFD and the only gas-rich one (
$M_\star = 2 \times 10^5 M_\odot$ ,$M_{\rm HI} = 4 \times 10^5 M_\odot$ ) - Searching for HI clouds with no optical SDSS counterpart. Found 5/29 detections (Janesh+ 2019) that typically have stellar masses 10x less than HI mass
(Tollerud) Implications for Reionization of a Search for Local Group Dwarfs with HI and Optical: Is There a Missing dIrr Problem?
- Using the ELVIS simulations (DM-only, LG-like)
- (Tollerud & Peek 2018) Extrapolate HI mass function (Bradford+ 2015) down to very low stellar masses, along with abundance matching, to assign gas and stellar masses to DM halos in the simulation
- Is there a missing dIrr problem? The LG is a <1/24 outlier? (SAGA?). The HI-Halo mass relation has a break? Reionization!
- There exists a cutoff halo mass at reionization where larger halos retain their gas.
- Using LG dwarfs, the cutoff mass is around
$10^9 M_\odot$ for a upper limit - Leo T HI mass gives us a lower limit. Combining them together gives a best cutoff estimate of 3 x 10$^8 M_\odot$, corresponding to
$10^{5-6} M_\odot$ in stellar mass
- At low halo masses, SN and radiative feedback will suppress galaxy formation
- (Bose+ 2018) Inspected how reionization timing affects the stellar mass fraction forming before reionization. Below
$10^{5-6} M_\odot$ is affected but above it isn't. - (Bose+ 2018) Predicts a UFD bump in the LF at z=0, where the bump's magnitude depends on the reionization redshift. The filtering mass changes the LF in a different way.
- Early forming massive galaxies have more UFDs.
- Only 3% of the MW-like halos in their SAM galaxies have both a LMC and a Gaia-Enceladus merger event
- Most UFDs in the simulations are within 50 kpc and more centrally concentrated in early-forming halos
- (Bose+ 2016) How does WDM affect the formation of galaxies and reionization?
- Results in gas-rich mergers and strong SF in halos just forming at the WDM cutoff mass, resulting in more faint UV sources at z>6 in the LF
- (Bose+ in prep) Reionization Illustris-TNG simulations with WDM. Possibility detectable in 21cm by its topology
- Coma Ber, Her, UMa (UFDs, M_V >~ -7) all have their SFHs halted before z=2. More classical dwarfs have extended SFHs
- (Skillman+ 2017) SFHs of 6 M31 satellites all with extended SFHs, but most form before z=0.5. They lie in a regime where the MW doesn't contain any similar dwarfs (in terms of SFH)
- (Weisz+ 2019) Obtained more SFHs of M31 satellites. The
$\tau_{90} - \tau_{50}$ plot is much different in M31 than the MW! Unclear why the differences. - (Gallart+ 2015; Albers+ 2019) Interesting to also look at SFHs that are isolated from MW or M31. Most are extended (but classical dwarfs)
- Focusing on Eri II. M$_V$ = -7.1, 366 kpc away. [Fe/H] = -2.38 with a 0.47 sigma in MDF. Very distant.
- Outside the virial radius of the MW but gas-poor, compared to the gas-rich dwarf Leo T, which is located at a slightly larger distance
- (Koposov+ 2015) Possible evidence for young stars and a nuclear cluster that is 14" (24pc) offset from the center (Simon+ in prep). Is this suggestive of a cored density profile?
- The stellar population is old, 13 Gyr, likely being quenched by reionization.
- It is making its first infall at its pericenter.
- Searching for Pop III chemical signatures in DLAs, using ejecta from Heger & Woosley (2010)
- Chemical signatures will likely be mixed in multiple minihalos. Underlying Pop III IMF is stochastically sampled. At small numbers, the [C/O] (for example) distribution is noisy, but it becomes more concentrated at some value (?) with more stars forming
- Current data: 11 most metal-poor DLAs at z>2.6. [Fe/H] = -3.45
$\rightarrow$ -2.5 - (Welsh+ 2019) Models indicate that a small number of stars (<72) enriched these DLAs with a maximum mass of 40
$M_\odot$ (Sukhbold+ 2016), and a typical explosion energy of 2e51 erg - Total stellar mass in DLAs are between 1000-3000 Msun, comparable to the faintest MW satellites that have
$10^2 - 10^5 M_\odot$ - Assuming 100% retention of metals, gas mass is around
$10^6 M_\odot$ or a 0.03% SF efficiency ($M_\star / M_{\rm gas}$ ) - Future work: extend analysis to EMP stars
- What can the most metal-poor stars tell us about the first stars? e.g. Chemical abundances, kinematics.
- (Starkenburg+ 2017) Where are the oldest stars? Note that the most metal-poor stars aren't the oldest stars. Look in the halo, the bulge, or the satellites.
- (Aguado+ 2017, 2018) Approaching at metallicity floor? 14 known [Fe/H] < -4.5 stars. Carbon is important. 1 in 80,000 have [Fe/H] < -4 (Youakim+ 2017)
- (Sestito+ 2019) Inspecting the kinematics (retrograde vs prograde orbits, vertical action space) of the MP stars. Most are actually in the disk plane! Is this evidence of early Galaxy build-up?
- EMP stars in dwarfs: (Starkenburg+ 2017, Ji+ 2019) Not yet in the [Fe/H] < -4 regime. Is this sampling or pre-enrichment? They are good testbeds for chemical evolution. More/less/same scatter in abundances?
- (Norris & Yong 2019) 1D-LTE vs 3D-LTE vs 3D-NLTE models can give different results between lines and actual metallicities.
- (Arentsen+ 2019) In binaries, one has to worry about binaries, especially AGB companion stars that can transfer s-elements and carbon.
- Good thing is that this can be checked with radial velocities.
- Ba-rich stars are in binaries, Ba-poor stars aren't. But Ba-poor stars can still be in binaries. Need to be careful about binary abundance patterns.
- Current work: most metal-poor stars, halo MDF, substructure within Galactic halo depending on metallicity, discriminate BHB stars
- Draco II: tiny in mass but large in size (being disrupted). Is it a dwarf or GC? [Fe/H] = -2.7 with a very small spread <0.15 dex (consistent with zero?), slightly larger than GCs
- Sgr II: [Fe/H] = -2.3 with a definite 0.15 dex spread
- Can't observe the first stars, so we need a different way to infer the properties of Pop III (use EMPs and metal-poor DLAs)
- If we use the dwarfs as a gateway to the first galaxies, there needs to be little SF at later times to isolate the ancient stellar population
- (Jeon+ 2017) Simulation: 2000
$M_\odot$ DM particles, Pop III + metal-enriched star formation modes, metal mixing with SPH - SF quenching at reionization in low-mass galaxies (<2e9
$M_\odot$ ). More massive halos hosted episodic SF at later times. Is there a distincition between UFDs and classical dwarfs on which ones were quenched or not? - CEMP stars formed from Pop III SN, whereas stars with typical chemical signatures were enriched from multiple populations
- (Jeon+ 2019) Examining a z=3 DLA in their simulation that includes Pop III stars. These EMP DLAs should only exist at high redshift (z>3)
- (Chiti+ submitted) Calculated grids for [Fe/H] and log g, focusing on metal-poor giants in Skymapper. Finds a larger scatter at [Fe/H] = -3 (sigma = 0.35) than at [Fe/H] = -2 (sigma = 0.16)
- (Chiti+ 2018) Tuc II. Found two members at ~2 half-light radii with [Fe/H] = -3.08 and -3.44. The whole system is very elongated. MDF with a peak at [Fe/H] = -3 with a secondary peak at -1.3 (unclear what can cause that)
- (Chiti & Frebel 2019) Sgr dSph. Found four new EMP stars. ~36% of EMP stars are all CEMP stars.
- (Brauer+ 2018) Model for r-process star formation in dwarfs with the Caterpillar simulations. 15% of all UFDs have r-process enrichment, and ~40% of classical dwarfs. 50% of r-II halo stars originated in small systems similar to Ret II.
- (Gull+ 2019) Searching for r-process stars in stellar systems. Found a high frequency of r-process stars. Stream progenitor (original stellar mass of
$10^8 M_\odot$ ) were unusually r-process rich (why?). - (Ezzeddine & Frebel 2018, 2019) Discovery of a star that was enriched by an aspherical (jet) explosion with a large explosion energy
- (Nordlander+ 2019) Lowest measured [Fe/H] abundance of -6.2. Found with Skymapper. Pop III fallback SN progenitor mass of 10-20
$M_\odot$ . [C/Fe] = -4, [Mg/Fe] = 0.6, [Ca/Fe] = 0.4
- UFDs are independent bursts of high-redshift SF
- (Ji+ in prep) Car II and III are bound to the LMC but are not related. They both have 12 stars with some (number?) having [Fe/H] < -3.5
- [Mg/Fe] declines much more rapidly versus [Fe/H] compare to [Ca/Fe], resulting in a steep [Mg/Ca] trend. This corresponds to the CCSN initial mass (McWilliam+ 2013).
- [Mg/Ca] > 0.2 (dominated by >20
$M_\odot$ CCSNe), [Mg/Ca] < -0.4 (dominated by <15$M_\odot$ CCSNe) - MW UFDs doesn't show this trend, whereas the LMC UFDs do. Environmental dependence on IMF? Inhomogenous mixing? Type Ia SNe with high Ca yields?
- (Ji+ 2016) r-process Ret II UFD. Most likely enriched by a single NS merger.
- New work: Measuring [Ba/H] scatter. Well-mixed metals (0.2 dex scatter) in a dilution gas mass of
$10^6 M_\odot$ . Flat trend$\rightarrow$ lack of pristine gas accretion?
- New work: Measuring [Ba/H] scatter. Well-mixed metals (0.2 dex scatter) in a dilution gas mass of
- (Ji+ in prep) Pop III IMF using CEMP stars and direct model fits using a grid of Pop III CCSN yields
- The most EMP stars have similar carbon abundances.
- The progenitor stellar masses are around 30
$M_\odot$ with a dilution mass between$10^4 - 10^5 M_\odot$ . - Chemical signatures in these UFDs similar to the MW halo EMPs
- FIRE-2 simulations of LMC (900
$M_\odot$ resolution) and MW/M31 (3500$M_\odot$ ) analogs - Latte suite (8 isolated MW-like systems) and ELVIS suite (3 LG-like suites)
- (Benincasa+ in prep) Studying massive GMCs in Latte sims. Finding excess of GMCs at their resolution limit (
$< 3 \times 10^5 M_\odot$ ). Cloud lifetimes 8-16 Myr. - (Loebman+ in prep) Studying massive star clusters in Latte sims. Finding slopes of -2.26 and -2.44 in their mass function (on the steep side when compared to observations).
- (Garrison-Kimmel+ 2019) Agreement of the satellite mass function of the Latte and ELVIS simulations with observations. In the MW-like simulations, the velocity profiles match observations, but there are no dense dwarf ellipticals in the M31 analog.
- (Samuel+ 2019) More rigrous test. The spatial distribution of satellites.
- Outside to 150kpc, the M31 and MW have similar radial distribution. But outside, the MW goes flat whereas M31 keeps on increasing
- The spread using many snapshots (time-averaging) from their suite sits right between the M31 and MW radial distributions
- The spread also broadly agrees with the SAGA survey
- They also searched their suite (over all time) for similar galaxies to the MW inner (<150 kpc) distribution, and none of them match in the outer regions
- (Jahn+ 2019) LMC-like galaxies. Little DM halo tidal destruction, especially compared to MW. A lot of the satellite mass functions are very steep below
$10^6 M_\odot$ compared to observations
(Pawlowski) Can we solve the planes of satellites galaxies problem of cosmology by invoking special host halo properties or baryonic effects?
- Planes of satellites problem: MW, M31, Cen A have flattened distributions of satellites and show signs of co-rotation. See Pawkowski (2018) for a review
- (Buck+ 2015; Pawlowski+ 2019) Searched ELVIS simulation suite for a relationship between satellite plane thickness and number of satellites.
- Didn't find correlations with (1) virial radius or (2) formation time, (3) anything special about M31/MW being a pair, or (4) baryonic physics
- (Pawlowski+ in prep) Looking motions around the orbital poles. 8/11 classical dwarfs do
- (Shao+ 2019) 8/11 classical dwarfs are co-rotating within 22 degrees, which is highly anisotropic
- Searched EAGLE for such a system. Only 1% have thin and co-rotating distribution of satellites. The rotation plane is aligned with the shape of the DM halo
- In one example, the inner halo is misaligned with the outer halo because of cosmic accretion, where the MW rotation is perpendicular to the MW disk.
- Inspecting NGC 147 & 185 - dense dwarf ellipticals in M31.
$V_{\rm circ} > 35$ km/s at r < 1 kpc. - NGC 147: younger system (mostly 5-7 Gyr stellar population), [Fe/H] = -1.3(?), tidal tail. NGC 185: older system (>8 Gyr), [Fe/H] = -1.1(?)
- The galaxies are moving in opposite directions with NGC 147 just passing through pericenter 300-500 Myr ago.
- Studying satellite kinematics through the clustering of orbital poles, reconstructing orbits, and velocity anisotropy
$\beta$ - Use APOSTLE and Auriga simulations to compare
$\beta$ likelihoods. - Assuming that the distribution is uniform, then
$\beta = 1.02 \pm 0.4$ , consistent (2$\sigma$) with Cautun & Frenk (2017). - Using the same 10 bright satellitles as Cautun & Frenk, then
$\beta = -1.52 \pm 1$ - Allowing for
$\beta$ to vary with radius, it is around -2 at 10-20 kpc, increasing to 0 at 100 kpc and +1 at 200 kpc. DM-only and APOSTLE simulations are all flat at zero, but Aurgia has a dip toward -1 at small radii. - GC and halo stars are more radial, agreeing with destruction of satellites on radial orbits
- Satellites closer to the center have more tangential motions, likely due to subhalo destruction from the central galaxy
- (Cautun+ 2019) LMC is usually massive for a MW-mass galaxy, having 5% of the MW stellar mass (Pennarubia+ 2016). Expected ~10% of similarly sized galaxies)
- Search for LMC-like galaxy in EAGLE with abundance matching, masses, and LMC+SMC pairs (only 2%). There are 36 counterparts with masses between
$2-4 \times 10^{11} M_\odot$ . - (Shao+ 2018) LMC analogs are bluer than field galaxies in EAGLE because of SF. Red simulated satellites are slow to quench.
- DM density wakes are created by infalling satellites but not observed yet.
- (Garavito+ 2019) N-body simulations. Calculating possible observables of the wake. At 45 and 70 kpc, the stellar wake is 60% more dense.
- At smaller (larger) radii, there are infall (outflow) from the wake as the stars cross the LMC orbital path
- BFE is a powerful tool to decompose the gravitational potential of th MW. Need 150 terms in the expansion to describe the potential. Finding the right number of terms is difficult (Weinberg 1998).
- Auriga simulations. The satellite luminosity function matches well with the MW down to
$M_V = -10$ . - Is the debris correlated in phase space longer than position space? Looking at binding energy and angular momentum (z-component in particular).
- Accreted material in galaxies shows a diversity of phase space structure, especially when a disk is accreted.
- To connect with Gaia results, they applied chemical cuts in Fe and Mg, which isolates a sample with 10% accreted material. This is better than a randomly selected sample.
- Comparing to SAGA, there are the right number of satellites, but the overall (what kind?) fraction is inconsistent.
- Using stellar streams to detect substructure. In a smooth potential, streams are smooth, but in a clumpy, time-evolving potential, the stream becomes irregular and has gaps.
- (Price-Whelan & Bonaca 2018) Inspecting the GD-1 stream, finding prominent gaps and stars outside the main stream.
- (Bonaca+ 2019) Perturbed stars creates a gap in the stream because of the altered orbital patterns.
- Qualitatively describes the GD-1 stream features
- Peturber properties: happened 500 Myr ago,
$5 \times 10^6 M_\odot$ ,$r_s \sim 10$ pc, 15 pc impact parameter, V = 250 km/s - Is marginally consistent with GC sizes and masses (but on the low-mass end), not DM subhalos
- However, tracing back the known GCs, their orbits have not crossed the stream
- (Bonaca+ in prep) Palomar 5 tidal stream. Has gaps and is asymmetric.
- (Drlica-Wagner+ 2019) LSST can detect
$10^5 M_\odot$ subhalos at some rate (see Erkal+ 2016)
- (Erkal+ 2015, Bonaca+ 2019, Erkal+ in prep) Possible to extract subhalo properties from the stream gaps
- (Bovy+ 2017) Also can fit the statistical properties of the stream (e.g. density) and extract perturber properties
- GD-1 stream gaps could be caused by an object that is much denser than a subhalo.
- Another model:
- Look at the spur that passes over the gap, where the stream width doubles at the stream-gap connection.
- Could the Sgr stream/dwarf affected GD-1 stream?
- Also, try to fit the gap/wiggle at -3 degrees. Still working on it, but it looks like a subhalo at
$10^{7-8} M_\odot$ .
- Can every stream be perturbed? Maybe... probably!
- There are ~1000 MW analogs (by mass) in Illustris-1.
- Observations show that stellar halos are aspherical because of projection effects (diversity in surface brightness).
- (Elias+ in prep) Inspecting the simulation data for analogs of the Gaia "sausage", which has a progenitor stellar mass
$3 \times 10^{8-9} M_\odot$ . - There are 37 MW analogs with a Gaia sauage merger that have a diversity in rotation, metallicity, and orbit of the infalling progenitor satellite.
- Note: Gaia Sausage and Gaia-Enceladus aren't the same but have significant overlap in their stellar debris.
(Laporte) Footprints of the Sagittarius dwarf in the Galactic disc from the outer disc to the 6-D Gaia Volume
- Ran N-body simulations of massive Sgr dwarf interaction with MW disk with different models (e.g. halo concentrations)
- (Laporte+ 2019) Many fine structures within the MW disk, flared and warped outer disk with "feathers" that might've been perturbed by Sgr dwarf
- Studying the anticenter stream, confirm the nature of the "feathers": kinematics, chemical composition (alpha vs Fe), older ages (by 3-5 Gyr)
- Last Sgr interaction resets any substructure that was induced by prior passages.
- (Shipp+ 2018, 2019) Measuring the proper motions of stellar systems, using DES and Gaia DR2
- S^5 survey [http://s5collab.github.io]
- Jhelum is a weird stream. 2 spatial components and 2 kinematic components with a wide scatter of metallicities and radial velocities.
- With the stream proper motions, one can determine the effects of the LMC -- that is, the stream velocities aren't aligned with their directions.
- Can be used to constrain the LMC mass and is consistent with previous results.
(Roederer) Chemically Tagging Remnants of Accreted Low-mass Dwarf Galaxies Using r-processenhanced Stars
- (Sneden+ 2008) A small fraction of metal-poor stars are highly enhanced by r-process elements.
- r-process stars aren't part of the MWdisk.
- (Roederer+ 2018) Compared the kinematics of the r-process stars with streams. All of the candidate groups show a small metallicity spread.
- Confirmed that r-process stars most likely came from disrupted UFDs (small pericenters)
- Abundance fitting sometimes is intractable with many degrees of freedom (i.e. many elements). However, it can be simplified with Fisher Information Matrix (a la CMB analysis)
- In practice: information lost, imperfect calibrations & models, model interpreation (nb: honest!)
pip install Chem-I-Calcto install his applet!- Github: [https://github.com/NathanSandford/Chem-I-Calc]
- (Cyburt+ 2015, Aver+ 2015) Using local dwarfs to constrain the primordial abundances that can be used in conjunction with the CMB
- With more targets and higher quality spectra, there will be tighter constraints, including
$N_{\rm eff}$
(Wechsler) The threshold of galaxy formation and the microphysics of dark matter from the tiniest galaxies
- Papers discussed: Nadler+ (2018, 2019ab)
- Modeling baryonic effects on subhalo populations with ML
- Modeling MW and subhalo populations
- Constraints on DM microphysics
- Many different DM models (CDM, SIDM, WDM, etc) are viable because they're not well-tested on small scales (Bullock & Moylan-Kolchin 2017)
- Halo-galaxy connection? Lowest mass halo that forms a galaxy? Stochasticity in low-mass galaxies?
- Do we understand the selection function of the discovered dwarfs?
- DES Y3 + PanSTARRS covers 82% of the non-dusty sky
- Recover all known satellites. No new discoveries.
- Selection function based on magnitude, size, and distance (will be released soon)
- (Mao+ 2015) Suite of MW-analog simulations, using the satellite-subhalo model (Nadler+ 2019)
- "Galaxy" means anything brighter than
$M_V = 0$ . - Take the satellite counts and occupation fraction and feed model through the selection function
- Split the sample between LMC and no-LMC populations
- Difficult to explain the anisotropy between DES and PS1 without the LMC, which boosts the counts dimmer than
$M_V = -6$ - 50% of
$3 \times 10^7 M_\odot$ ($2 \times 10^8 M_\odot$ at 2$\sigma$) halos are occupied - Baryonic effects are important
- Many MW satellites are still missing! Especially LSB ones.
- "Galaxy" means anything brighter than
- What does this tell us about DM? Constrains the DM scattering cross-section (1000x better than CMB even with pre-DES data)
- Entertaining and insightful overview with a far-reaching historical recount of the evolution of the "problems". No notes. Sorry!