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The star formation and gas content of satellite galaxies around the Milky Way (MW) and Andromeda (M31) are depleted relative to more isolated galaxies in the Local Group (LG) at fixed stellar mass. We explore the environmental regulation of gas content and quenching of star formation in $z=0$ galaxies at $M*=10^{5-10}\rm{M}_{\odot}$ around 14 MW-mass hosts from the FIRE-2 simulations. Lower-mass satellites ($M*\lesssim10^7\rm{M}_{\odot}$) are mostly quiescent and higher-mass satellites ($M*\gtrsim10^8\rm{M}_{\odot}$) are mostly star-forming, with intermediate-mass satellites ($M*\approx10^{7-8}\rm{M}_{\odot}$) split roughly equally between quiescent and star-forming. Hosts with more gas in their circumgalactic medium have a higher quiescent fraction of massive satellites ($M*=10^{8-9}\rm{M}_{\odot}$). We find no significant dependence on isolated versus paired (LG-like) host environments, and the quiescent fractions of satellites around MW-mass and LMC-mass hosts from the FIRE-2 simulations are remarkably similar. Environmental effects that lead to quenching can also occur as preprocessing in low-mass groups prior to MW infall. Lower-mass satellites typically quenched before MW infall as central galaxies or rapidly during infall into a low-mass group or a MW-mass galaxy. Most intermediate- to high-mass quiescent satellites have experienced $\geq1-2$ pericentre passages ($\approx2.5-5$ Gyr) within a MW-mass halo. Most galaxies with $M*\gtrsim10^{6.5}\rm{M}_{\odot}$ did not quench before falling into a host, indicating a possible upper mass limit for isolated quenching. The simulations reproduce the average trend in the LG quiescent fraction across the full range of satellite stellar masses. Though the simulations are consistent with the SAGA survey's quiescent fraction at $M*\gtrsim10^8\rm{M}_{\odot}$, they do not generally reproduce SAGA's turnover at lower masses., Comment: 17 pages, 13 figures, + appendices. Accepted by MNRAS

The orbits of satellite galaxies encode rich information about their histories. We investigate the orbital dynamics and histories of satellite galaxies around Milky Way (MW)-mass host galaxies using the FIRE-2 cosmological simulations, which, as previous works have shown, produce satellite mass functions and spatial distributions that broadly agree with observations. We first examine trends in orbital dynamics at z = 0, including total velocity, specific angular momentum, and specific total energy: the time of infall into the MW-mass halo primarily determines these orbital properties. We then examine orbital histories, focusing on the lookback time of first infall into a host halo and pericenter distances, times, and counts. Roughly 37 per cent of galaxies with Mstar < 10^7 Msun were `pre-processed' as a satellite in a lower-mass group, typically ~2.7 Gyr before falling into the MW-mass halo. Half of all satellites at z = 0 experienced multiple pericenters about their MW-mass host. Remarkably, for most (67 per cent) of these satellites, their most recent pericenter was not their minimum pericenter: the minimum typically was ~40 per cent smaller and occurred ~6 Gyr earlier. These satellites with growing pericenters appear to have multiple origins: for about half, their specific angular momentum gradually increased over time, while for the other half, most rapidly increased near their first apocenter, suggesting that a combination of a time-dependent MW-mass halo potential and dynamical perturbations in the outer halo caused these satellites' pericenters to grow. Our results highlight the limitations of idealized, static orbit modeling, especially for pericenter histories., 21 pages, 10 figues, 2 appendices, 4 appendix figures. Accepted in MNRAS for publication

We examine the prevalence, longevity, and causes of planes of satellite dwarf galaxies, as observed in the Local Group. We use 14 Milky Way/Andromeda-(MW/M31) mass host galaxies from the FIRE-2 simulations. We select the 14 most massive satellites by stellar mass within 300 kpc of each host and correct for incompleteness from the foreground galactic disc when comparing to the MW. We find that MW-like planes as spatially thin and/or kinematically coherent as observed are uncommon, but they do exist in our simulations. Spatially thin planes occur in 1-2 per cent of snapshots during $z=0-0.2$, and kinematically coherent planes occur in 5 per cent of snapshots. These planes are generally transient, surviving for less than 500 Myr. However, if we select hosts with an LMC-like satellite near first pericentre, the fraction of snapshots with MW-like planes increases dramatically to 7-16 per cent, with lifetimes of 0.7-1 Gyr, likely because of group accretion of satellites. We find that M31's satellite distribution is much more common: M31's satellites lie within about 1 sigma of the simulation median for every plane metric we consider. We find no significant difference in average satellite planarity for isolated hosts versus hosts in LG-like pairs. Baryonic and dark matter-only simulations exhibit similar levels of planarity, even though baryonic subhaloes are less centrally concentrated within their host haloes. We conclude that planes of satellites are not a strong challenge to LCDM cosmology., Comment: 15 pages, 8 figures. Main results in Figures 2 and 7. Accepted by MNRAS

We present new chemo--kinematics of the Hercules dwarf galaxy based on Keck II-- DEIMOS spectroscopy. Our 21 confirmed members have a systemic velocity of $v_{\mathrm{Herc}}=46.4\pm1.3$ kms$^{-1}$ and a velocity dispersion $\sigma_{v,\mathrm{Herc}}=4.4^{+1.4}_{-1.2}$ kms$^{-1}$. From the strength of the Ca II triplet, we obtain a metallicity of [Fe/H]= $-2.48\pm0.19$ dex and dispersion of $\sigma_{\rm{[Fe/H]}}= 0.63^{+0.18}_{-0.13}$ dex. This makes Hercules a particularly metal--poor galaxy, placing it slightly below the standard mass--metallicity relation. Previous photometric and spectroscopic evidence suggests that Hercules is tidally disrupting and may be on a highly radial orbit. From our identified members, we measure no significant velocity gradient. By cross--matching with the second \textit{Gaia} data release, we determine an uncertainty--weighted mean proper motion of $\mu_{\alpha}^*=\mu_{\alpha}\cos(\delta)=-0.153\pm{0.074}$ mas yr$^{-1}$, $\mu_{\delta}=-0.397\pm0.063$ mas yr$^{-1}$. This proper motion is slightly misaligned with the elongation of Hercules, in contrast to models which suggest that any tidal debris should be well aligned with the orbital path. Future observations may resolve this tension., Comment: Submitted to MNRAS. 17 pages, 14 figures

PetroFit is an open-source Python package, based on Astropy and Photutils, that can calculate Petrosian profiles and fit galaxy images. It offers end-to-end tools for making accurate photometric measurements, estimating morphological properties, and fitting 2D models to galaxy images. Petrosian metric radii can be used for model parameter estimation and aperture photometry to provide accurate total fluxes. Correction tools are provided for improving Petrosian radii estimates affected by galaxy morphology. PetroFit also provides tools for sampling Astropy-based models (including custom profiles and multi-component models) onto image grids and enables PSF convolution to account for the effects of seeing. These capabilities provide a robust means of modeling and fitting galaxy light profiles. We have made the PetroFit package publicly available on GitHub (PetroFit/petrofit) and PyPi (pip install petrofit)., Comment: Published AJ, 28 pages, 17 figures, see https://github.com/PetroFit/petrofit; typos corrected, footnote on PSFModel class, paper status update, DOI provided

We use globular cluster data from the Resolved Stellar Populations Early Release Science (ERS) program to validate the flux calibration for the Near Infrared Camera (NIRCam) on the James Webb Space Telescope (JWST). We find a significant flux offset between the eight short wavelength detectors, ranging from 1-23% (about 0.01-0.2 mag) that affects all NIRCam imaging observations. We deliver improved zeropoints for the ERS filters and show that alternate zeropoints derived by the community also improve the calibration significantly. We also find that the detector offsets appear to be time variable by up to at least 0.1 mag., Comment: Accepted for publication in RNAAS

We present initial results from a large spectroscopic survey of stars throughout M33's stellar disk. We analyze a sample of 1667 red giant branch (RGB) stars extending to projected distances of $\sim 11$ kpc from M33's center ($\sim 18$ kpc, or $\sim 10$ scale lengths, in the plane of the disk). The line-of-sight velocities of RGB stars show the presence of two kinematical components. One component is consistent with rotation in the plane of M33's HI disk and has a velocity dispersion ($\sim 19$ km s$^{-1}$) consistent with that observed in a comparison sample of younger stars, while the second component has a significantly higher velocity dispersion. A two-component fit to the RGB velocity distribution finds that the high dispersion component has a velocity dispersion of $59.3^{+2.6}_{-2.5}$ km s$^{-1}$ and rotates very slowly in the plane of the disk (consistent with no rotation at the $, Comment: 33 pages, 19 figures. Accepted for publication in ApJ

We present the color-magnitude diagrams and star formation histories (SFHs) of seven ultra-faint dwarf galaxies: Horologium 1, Hydra 2, Phoenix 2, Reticulum 2, Sagittarius 2, Triangulum 2, and Tucana 2, derived from high-precision Hubble Space Telescope photometry. We find that the SFH of each galaxy is consistent with them having created at least 80% of the stellar mass by $z\sim6$. For all galaxies, we find quenching times older than 11.5 Gyr ago, compatible with the scenario in which reionization suppresses the star formation of small dark matter halos. However, our analysis also reveals some differences in the SFHs of candidate Magellanic Cloud satellites, i.e., galaxies that are likely satellites of the Large Magellanic Cloud and that entered the Milky Way potential only recently. Indeed, Magellanic satellites show quenching times about 600 Myr more recent with respect to those of other Milky Way satellites, on average, even though the respective timings are still compatible within the errors. This finding is consistent with theoretical models that suggest that satellites' SFHs may depend on their host environment at early times, although we caution that within the error bars all galaxies in our sample are consistent with being quenched at a single epoch., 7 pages, 3 figures, 2 tables. Accepted for publication in ApJL

We present deep Hubble Space Telescope (HST) photometry of the ultra-faint dwarf (UFD) galaxies Pegasus III (Peg III) and Pisces II (Psc II), two of the most distant satellites in the halo of the Milky Way (MW). We measure the structure of both galaxies, derive mass-to-light ratios with newly determined absolute magnitudes, and compare our findings to expectations from UFD-mass simulations. For Peg III, we find an elliptical half-light radius of $a_h{{=}}1.88^{+0.42}_{-0.33}$ arcminutes ($118^{+31}_{-30}$ pc) and $M_V{=}{-4.17}^{+0.19}_{-0.22}$; for Psc II, we measure $a_h{=}1.31^{+0.10}_{-0.09}$ arcminutes ($69\pm8$ pc) and $M_V{=}{-4.28}^{+0.19}_{-0.16}$. We do not find any morphological features that indicate a significant interaction between the two has occurred, despite their close separation of only $\sim$40 kpc. Using proper motions (PMs) from Gaia early Data Release 3, we investigate the possibility of any past association by integrating orbits for the two UFDs in a MW-only and a combined MW and Large Magellanic Cloud (LMC) potential. We find that including the gravitational influence of the LMC is crucial, even for these outer-halo satellites, and that a possible orbital history exists where Peg III and Psc II experienced a close ($\sim$10-20 kpc) passage about each other just over $\sim$1 Gyr ago, followed by a collective passage around the LMC ($\sim$30-60 kpc) just under $\sim$1 Gyr ago. Considering the large uncertainties on the PMs and the restrictive priors imposed to derive them, improved PM measurements for Peg III and Psc II will be necessary to clarify their relationship. This would add to the rare findings of confirmed pairs of satellites within the Local Group., Comment: 18 pages, 11 figures; submitted to ApJ

The gas content of the complete compilation of Local Group dwarf galaxies (119 within 2 Mpc) is presented using HI survey data. Within the virial radius of the Milky Way (224 kpc here), 53 of 55 dwarf galaxies are devoid of gas to limits of M$_{\rm HI}, 26 pages, 7 figures, 3 tables, Accepted by ApJ

Andromeda XXI (And XXI) has been proposed as a dwarf spheroidal galaxy with a central dark matter density that is lower than expected in the Standard $\Lambda$ Cold Dark Matter ($\Lambda$CDM) cosmology. In this work, we present dynamical observations for 77 member stars in this system, more than doubling previous studies to determine whether this galaxy is truly a low density outlier. We measure a systemic velocity of $v_r=-363.4\pm1.0\,{\rm kms}^{-1}$ and a velocity dispersion of $\sigma_v=6.1^{+1.0}_{-0.9}\,{\rm kms}^{-1}$, consistent with previous work and within $1\sigma$ of predictions made within the modified Newtonian dynamics framework. We also measure the metallicity of our member stars from their spectra, finding a mean value of ${\rm [Fe/H]}=-1.7\pm0.1$~dex. We model the dark matter density profile of And~XXI using an improved version of \GravSphere, finding a central density of $\rho_{\rm DM}({\rm 150 pc})=2.7_{-1.7}^{+2.7} \times 10^7 \,{\rm M_\odot\,kpc^{-3}}$ at 68\% confidence, and a density at two half light radii of $\rho_{\rm DM}({\rm 1.75 kpc})=0.9_{-0.2}^{+0.3} \times 10^5 \,{\rm M_\odot\,kpc^{-3}}$ at 68\% confidence. These are both a factor ${\sim}3-5$ lower than the densities expected from abundance matching in $\Lambda$CDM. We show that this cannot be explained by `dark matter heating' since And~XXI had too little star formation to significantly lower its inner dark matter density, while dark matter heating only acts on the profile inside the half light radius. However, And~XXI's low density can be accommodated within $\Lambda$CDM if it experienced extreme tidal stripping (losing $>95\%$ of its mass), or if it inhabits a low concentration halo on a plunging orbit that experienced repeated tidal shocks., Comment: Accepted to MNRAS, 17 pages, 12 figures

We present a Bayesian method to identify multiple (chemodynamic) stellar populations in dwarf spheroidal galaxies (dSphs) using velocity, metallicity, and positional stellar data without the assumption of spherical symmetry. We apply this method to a new Keck/DEIMOS spectroscopic survey of the Ursa Minor (UMi) dSph. We identify 892 likely members, making this the largest UMi sample with line-of-sight velocity and metallicity measurements. Our Bayesian method detects two distinct chemodynamic populations with high significance ($\ln{B}\sim33$). The metal-rich ($[{\rm Fe/H}]=-2.05\pm0.03$) population is kinematically colder (radial velocity dispersion of $\sigma_v=4.9\pm0.8 \, {\rm km \, s^{-1}}$) and more centrally concentrated than the metal-poor ($[{\rm Fe/H}]=-2.29\pm0.05$) and kinematically hotter population ($\sigma_v =11.5\pm0.9\, {\rm km \, s^{-1}}$). Furthermore, we apply the same analysis to an independent MMT/Hectochelle data set and confirm the existence of two chemodynamic populations in UMi. In both data sets, the metal-rich population is significantly flattened ($\epsilon=0.75\pm0.03$) and the metal-poor population is closer to spherical ($\epsilon=0.33_{-0.09}^{+0.12}$). Despite the presence of two populations, we are unable to robustly estimate the slope of the dynamical mass profile. We found hints for prolate rotation of order $\sim 2 \, {\rm km \, s^{-1}}$ in the MMT data set, but further observations are required to verify this. The flattened metal-rich population invalidates assumptions built into simple dynamical mass estimators, so we computed new astrophysical dark matter annihilation (J) and decay profiles based on the rounder, hotter metal-poor population and inferred $\log_{10}{(J(0.5^{\circ})/{\rm GeV^{2} \, cm^{-5}})}\approx19.1$ for the Keck data set. Our results paint a more complex picture of the evolution of Ursa Minor than previously discussed., Comment: 20 pages, 11 figures, data included. Comments welcome. Accepted to MNRAS

Full list of authors: Cerny, W.; Pace, A. B.; Drlica-Wagner, A.; Koposov, S. E.; Vivas, A. K.; Mau, S.; Riley, A. H.; Bom, C. R.; Carlin, J. L.; Choi, Y.; Erkal, D.; Ferguson, P. S.; James, D. J. ; Li, T. S.; Martínez-Delgado, D.; Martínez-Vázquez, C. E.; Munoz, R. R.; Mutlu-Pakdil, B.; Olsen, K. A. G.; Pieres, A.; Sakowska, J. D.; Sand, D. J.; Simon, J. D.; Smercina, A.; Stringfellow, G. S.; Tollerud, E. J.; Adamów, M.; Hernandez-Lang, D.;Kuropatkin, N.; Santana-Silva, L.; Tucker, D. L.; Zenteno, A.; Delve Collaboration., We present the discovery of a candidate ultra-faint Milky-Way satellite, Eridanus IV (DELVE J0505-0931), detected in photometric data from the DECam Local Volume Exploration survey (DELVE). Eridanus IV is a faint (MV = - 4.7 ± 0.2), extended ( = - r 75+ pc 1 2 13 16 ), and elliptical (ò = 0.54 ± 0.1) system at a heliocentric distance of - 76.7+ kpc 6.1 4.0 , with a stellar population that is well described by an old, metal-poor isochrone (age of τ ∼ 13.0 Gyr and metallicity of [Fe/H] - 2.1 dex). These properties are consistent with the known population of ultra-faint Milky-Way satellite galaxies. Eridanus IV is also prominently detected using proper-motion measurements from Gaia Early Data Release 3, with a systemic proper motion of (ma cos d, md) = (+0.25 0.06, -0.10 0.05) mas yr-1 measured from its horizontal branch and red-giant-branch member stars. We find that the spatial distribution of likely member stars hints at the possibility that the system is undergoing tidal disruption. © 2021 Institute of Physics Publishing. All rights reserved., The DELVE project is partially supported by Fermilab LDRD project L2019-011 and the NASA Fermi Guest Investigator Program Cycle 9 No. 91201. A.B.P. acknowledges support from NSF grant AST-1813881. This research received support from the National Science Foundation (NSF) under grant No. NSF DGE-1656518 through the NSF Graduate Research Fellowship received by S.M. B.M.P. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-2001663. J.L.C. acknowledges support from NSF grant AST-1816196. J.D.S. acknowledges support from NSF grant AST-1714873. S.R.M. acknowledges support from NSF grant AST-1909497. D.M.D. acknowledges financial support from the Talentia Senior Program (through the incentive ASE-136) from Secretaria General de Universidades, Investigacion y Tecnologia, de la Junta de Andalucia. This project used data obtained with the Dark Energy Camera (DECam), which was constructed by the Dark Energy Survey (DES) collaboration. Funding for the DES Projects has been provided by the DOE and NSF (USA), MISE (Spain), STFC (UK), HEFCE (UK), NCSA (UIUC), KICP (U. Chicago), CCAPP (Ohio State), MIFPA (Texas A&M University), CNPQ, FAPERJ, FINEP (Brazil), MINECO (Spain), DFG (Germany), and the collaborating institutions in the Dark Energy Survey, which are Argonne Lab, UC Santa Cruz, University of Cambridge, CIEMAT-Madrid, University of Chicago, University College London, DES-Brazil Consortium, University of Edinburgh, ETH Zurich, Fermilab, University of Illinois, ICE (IEEC-CSIC), IFAE Barcelona, Lawrence Berkeley Lab, LMU Munchen, and the associated Excellence Cluster Universe, University of Michigan, NSF's National Optical-Infrared Astronomy Research Laboratory, University of Nottingham, Ohio State University, OzDES Membership Consortium University of Pennsylvania, University of Portsmouth, SLAC National Lab, Stanford University, University of Sussex, and Texas A&M University. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium).Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This manuscript has been authored by Fermi Research Alliance, LLC, under contract No. DE-AC02-07CH11359 with the US Department of Energy, Office of Science, Office of High Energy Physics. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes., With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.

This white paper offers guidance and ideas for how we can evolve our technical and collaborative frameworks to promote efficient algorithmic development and take advantage of opportunities for scientific discovery in the petabyte era.

We present the Stage II results from the ongoing Satellites Around Galactic Analogs (SAGA) Survey. Upon completion, the SAGA Survey will spectroscopically identify satellite galaxies brighter than $ M_{r,o} = -12.3 $ around 100 Milky Way (MW) analogs at $ z \sim 0.01 $. In Stage II, we have more than quadrupled the sample size of Stage I, delivering results from 127 satellites around 36 MW analogs with an improved target selection strategy and deep photometric imaging catalogs from the Dark Energy Survey and the Legacy Surveys. We have obtained 25,372 galaxy redshifts, peaking around $ z = 0.2 $. These data significantly increase spectroscopic coverage for very low redshift objects in $ 17 < r_o < 20.75 $ around SAGA hosts, creating a unique data set that places the Local Group in a wider context. The number of confirmed satellites per system ranges from zero to nine, and correlates with host galaxy and brightest satellite luminosities. We find that the number and the luminosities of MW satellites are consistent with being drawn from the same underlying distribution as SAGA systems. The majority of confirmed SAGA satellites are star forming, and the quenched fraction increases as satellite stellar mass and projected radius from the host galaxy decrease. Overall, the satellite quenched fraction among SAGA systems is lower than that in the Local Group. We compare the luminosity functions and radial distributions of SAGA satellites with theoretical predictions based on cold dark matter simulations and an empirical galaxy-halo connection model and find that the results are broadly in agreement., 42 pages, 22 figures, 3 tables. See Sec. 9 (p.28) for summary and figure index. Main results are shown in Sec. 6-8 (Fig. 8-18). Accepted by ApJ. Data available on survey website: https://sagasurvey.org

We study ram pressure stripping in simulated Milky Way-like halos at z>=2 from the Figuring Out Gas & Galaxies In Enzo (FOGGIE) project. These simulations reach exquisite resolution in their circumgalactic medium (CGM) gas owing to FOGGIE's novel refinement scheme. The CGM of each halo spans a wide dynamic range in density and velocity over its volume---roughly 6 dex and 1000 km/s, respectively---translating into a 5 dex range in ram pressure imparted to interacting satellites. The ram pressure profiles of the simulated CGM are highly stochastic, owing to kpc-scale variations of the density and velocity fields of the CGM gas. As a result, the efficacy of ram pressure stripping depends strongly on the specific path a satellite takes through the CGM. The ram-pressure history of a single satellite is generally unpredictable and not well correlated with its approach vector with respect to the host galaxy. The cumulative impact of ram pressure on the simulated satellites is dominated by only a few short strong impulses---on average, 90% of the total surface momentum gained through ram pressure is imparted in 20% or less of the total orbital time. These results reveal an erratic mode of ram pressure stripping in Milky-Way like halos at high redshift---one that is not captured by a smooth spherically-averaged model of the circumgalactic medium., 18 pages, 10 figures. Submitted to ApJ

Dedicated HI surveys have recently led to a growing category of low-mass galaxies found in the Local Volume. We present synthesis imaging of one such galaxy, Pisces A, a low-mass dwarf originally confirmed via optical imaging and spectroscopy of neutral hydrogen (HI) sources in the Galactic Arecibo L-band Feed Array HI (GALFA-HI) survey. Using HI observations taken with the Karl G. Jansky Very Large Array (JVLA), we characterize the kinematic structure of the gas and connect it to the galaxy's environment and evolutionary history. While the galaxy shows overall ordered rotation, a number of kinematic features indicate a disturbed gas morphology. These features are suggestive of a tumultuous recent history, and represent $\sim 3.5$% of the total baryonic mass. We find a total baryon fraction $f_{\rm bary} = 0.13$ if we include these features. We also quantify the cosmic environment of Pisces A, finding an apparent alignment of the disturbed gas with nearby, large scale filamentary structure at the edge of the Local Void. We consider several scenarios for the origin of the disturbed gas, including gas stripping via ram pressure or galaxy-galaxy interactions, as well as accretion and ram pressure compression. Though we cannot rule out a past interaction with a companion, our observations best support the suggestion that the neutral gas morphology and recent star formation in Pisces A is a direct result of its interactions with the IGM., Comment: 16 pages, 12 figures, accepted to ApJ

With a central surface brightness of $\mu_0=29.3$ mag. per sq. arcsec, and half-light radius of $r_{\rm half}=3.1^{+0.9}_{-1.1}$~kpc, Andromeda XIX (And XIX) is an extremely diffuse satellite of Andromeda. We present spectra for $\sim100$ red giant branch stars in this galaxy, plus 16 stars in a nearby stellar stream. With this exquisite dataset, we re-derive the properties of And XIX, measuring a systemic velocity of $v_r=-109.0\pm1.6$ km/s and a velocity dispersion of $\sigma_v = 7.8^{+1.7}_{-1.5}$ km/s (higher than derived in our previous work). We marginally detect a velocity gradient along the major axis of ${\rm d}v/{\rm d}r = -2.1\pm1.8$ km/s kpc$^{-1}$. We find its mass-to-light ratio is higher than galaxies of comparable stellar mass ($[M/L]_{\rm half} = 278^{+146}_{-198}M_\odot/L_\odot$), but its dynamics place it in a halo with a similar total mass to these galaxies. This could suggest that And XIX is a "puffed up" dwarf galaxy, whose properties have been altered by tidal processes, similar to its Milky Way counterpart, Antlia II. For the nearby stream, we measure $v_r=-279.2\pm3.7$ km/s, and $\sigma_v=13.8^{+3.5}_{-2.6}$ km/s. We measure its metallicity, and find it to be more metal rich than And XIX, implying that the two features are unrelated. Finally, And XIX's dynamical and structural properties imply it is a local analogue to ultra diffuse galaxies (UDGs). Its complex dynamics suggest that the masses of distant UDGs measured from velocity dispersions alone should be carefully interpreted, Comment: 15 pages, (plus 5 extra for appendices), 15 figures, MNRAS accepted (no significant revision from previous version)

We present a deep Hubble Space Telescope (HST) imaging study of two dwarf galaxies in the halos of Local Volume Large Magellanic Cloud (LMC) analogs. These dwarfs were discovered as part of our Subaru+Hyper Suprime-Cam MADCASH survey: MADCASH-1, which is a satellite of NGC 2403 (D~3.2 Mpc), and MADCASH-2, a previously unknown dwarf galaxy near NGC 4214 (D~3.0 Mpc). Our HST data reach >3.5 mag below the tip of the red giant branch (TRGB) of each dwarf, allowing us to derive their structural parameters and assess their stellar populations. We measure TRGB distances ($D=3.41^{+0.24}_{-0.23}$ Mpc for MADCASH-1, and $D=3.00^{+0.13}_{-0.15}$ Mpc for MADCASH-2), and confirm their associations with their host galaxies. MADCASH-1 is a predominantly old, metal-poor stellar system (age ~13.5 Gyr, [M/H] ~ -2.0), similar to many Local Group dwarfs. Modelling of MADCASH-2's CMD suggests that it contains mostly ancient, metal-poor stars (age ~13.5 Gyr, [M/H] ~ -2.0), but that ~10% of its stellar mass was formed 1.1--1.5 Gyr ago, and ~1% was formed 400--500 Myr ago. Given its recent star formation, we search MADCASH-2 for neutral hydrogen using the Green Bank Telescope, but find no emission and estimate an upper limit on the HI mass of $, 20 pages, 9 figures, 4 tables; minor edits to match accepted version published in ApJ

We present chemical abundances of red giant branch (RGB) stars in the dwarf spheroidal (dSph) satellite system of Andromeda (M31), using spectral synthesis of medium resolution (R $\sim 6000$) spectra obtained with the Keck II telescope and DEIMOS spectrograph via the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo (SPLASH) survey. We coadd stars according to their similarity in photometric metallicity or effective temperature to obtain a signal-to-noise ratio (S/N) high enough to measure average [Fe/H] and [$\alpha$/Fe] abundances. We validate our method using high S/N spectra of RGB stars in Milky Way globular clusters as well as deep observations for a subset of the M31 dSphs in our sample. For this set of validation coadds, we compare the weighted average abundance of the individual stars with the abundance determined from the coadd. We present individual and coadded measurements of [Fe/H] and [$\alpha$/Fe] for stars in ten M31 dSphs, including the first [$\alpha$/Fe] measurements for And IX, XIV, XV, and XVIII. These fainter, less massive dSphs show declining [$\alpha$/Fe] relative to [Fe/H], implying an extended star formation history. In addition, these dSphs also follow the same mass-metallicity relation found in other Local Group satellites. The conclusions we infer from coadded spectra agree with those from previous measurements in brighter M31 dSphs with individual abundance measurements, as well as conclusions from photometric studies. These abundances greatly increase the number of spectroscopic measurements of the chemical composition of M31's less massive dwarf satellites, which are crucial to understanding their star formation history and interaction with the M31 system., Comment: 34 pages, 17 figures. Submitted to ApJ

94 pages, 22 figures, 1 table; Astrophysical and cosmological observations currently provide the only robust, empirical measurements of dark matter. Future observations with Large Synoptic Survey Telescope (LSST) will provide necessary guidance for the experimental dark matter program. This white paper represents a community effort to summarize the science case for studying the fundamental physics of dark matter with LSST. We discuss how LSST will inform our understanding of the fundamental properties of dark matter, such as particle mass, self-interaction strength, non-gravitational couplings to the Standard Model, and compact object abundances. Additionally, we discuss the ways that LSST will complement other experiments to strengthen our understanding of the fundamental characteristics of dark matter. More information on the LSST dark matter effort can be found at https://lsstdarkmatter.github.io/ .

In recent years, ultrafaint dwarf (UFD) galaxies have been found through systematic searches of large optical surveys. However, the existence of Leo T, a nearby gas-rich dwarf, suggests that there could be other nearby UFDs that are optically obscured but have gas detectable at nonoptical wavelengths. With this in mind, we perform a search of the full Galactic Arecibo $L-$band Feed Array HI (GALFA-HI) survey, a radio survey which covers one-third of the sky at velocities $-650 < V_{\rm{LSR}} < +650 \; \rm{km} \; \rm{s^{-1}}$, for neutral hydrogen sources. We are able to probe regions of the sky at lower Galactic latitudes and smaller $|V_{LSR}|$ compared to previous explorations. We use the Source Finding Application (SoFiA) on GALFA-HI and select all sources with similar properties to Leo T and other local dwarf galaxies. We find 690 dwarf galaxy candidates, one of which is particularly promising and likely a new galaxy near the Galactic plane ($b=-8^{\circ}$) that is comparable in velocity width and HI-flux to other recently discovered local volume galaxies. We find we are sensitive to Leo T-like objects out to $1 \; \rm{Mpc}$ at velocities clear from background HI emission. We check each candidate's corresponding optical fields from Pan-STARRS and fit stars drawn from isochrones, but find no evidence of stellar populations. We thus find no other Leo T-like dwarfs within $500 \; \rm{kpc}$ of the Milky Way in the one-third of the sky covered by the GALFA-HI footprint and discuss our nondetection in a cosmological context., Accepted to ApJ. 14 pages, 10 figures. Table 2 is available in its entirety as an ancillary file on this page

We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local Volume Exploration survey (DELVE). The first system, Centaurus I (DELVE J1238-4054), is identified as a resolved overdensity of old and metal-poor stars with a heliocentric distance of ${\rm D}_{\odot} = 116.3_{-0.6}^{+0.6}$ kpc, a half-light radius of $r_h = 2.3_{-0.3}^{+0.4}$ arcmin, an age of $\tau > 12.85$ Gyr, a metallicity of $Z = 0.0002_{-0.0002}^{+0.0001}$, and an absolute magnitude of $M_V = -5.55_{-0.11}^{+0.11}$ mag. This characterization is consistent with the population of ultra-faint satellites, and confirmation of this system would make Centaurus I one of the brightest recently discovered ultra-faint dwarf galaxies. Centaurus I is detected in Gaia DR2 with a clear and distinct proper motion signal, confirming that it is a real association of stars distinct from the Milky Way foreground; this is further supported by the clustering of blue horizontal branch stars near the centroid of the system. The second system, DELVE 1 (DELVE J1630-0058), is identified as a resolved overdensity of stars with a heliocentric distance of ${\rm D}_{\odot} = 19.0_{-0.6}^{+0.5} kpc$, a half-light radius of $r_h = 0.97_{-0.17}^{+0.24}$ arcmin, an age of $\tau = 12.5_{-0.7}^{+1.0}$ Gyr, a metallicity of $Z = 0.0005_{-0.0001}^{+0.0002}$, and an absolute magnitude of $M_V = -0.2_{-0.6}^{+0.8}$ mag, consistent with the known population of faint halo star clusters. Given the low number of probable member stars at magnitudes accessible with Gaia DR2, a proper motion signal for DELVE 1 is only marginally detected. We compare the spatial position and proper motion of both Centaurus I and DELVE 1 with simulations of the accreted satellite population of the Large Magellanic Cloud (LMC) and find that neither is likely to be associated with the LMC., Comment: 17 pages, 6 figures, 1 table; updated to match published version; updated to address erratum

We present models of the H$\beta$-emitting broad-line region (BLR) in seven Seyfert 1 galaxies from the Lick AGN (Active Galactic Nucleus) Monitoring Project 2011 sample, drawing inferences on the BLR structure and dynamics as well as the mass of the central supermassive black hole. We find that the BLR is generally a thick disk, viewed close to face-on, with preferential emission back toward the ionizing source. The dynamics in our sample range from near-circular elliptical orbits to inflowing or outflowing trajectories. We measure black hole masses of $\log_{10}(M_{\rm BH}/M_\odot) = 6.48^{+0.21}_{-0.18}$ for PG 1310$-$108, $7.50^{+0.25}_{-0.18}$ for Mrk 50, $7.46^{+0.15}_{-0.21}$ for Mrk 141, $7.58^{+0.08}_{-0.08}$ for Mrk 279, $7.11^{+0.20}_{-0.17}$ for Mrk 1511, $6.65^{+0.27}_{-0.15}$ for NGC 4593, and $6.94^{+0.14}_{-0.14}$ for Zw 229$-$015. We use these black hole mass measurements along with cross-correlation time lags and line widths to recover the scale factor $f$ used in traditional reverberation mapping measurements. Combining our results with other studies that use this modeling technique, bringing our sample size to 16, we calculate a scale factor that can be used for measuring black hole masses in other reverberation mapping campaigns. When using the root-mean-square (rms) spectrum and using the line dispersion to measure the line width, we find $\log_{10}(f_{{\rm rms},\sigma})_{\rm pred} = 0.57 \pm 0.19$. Finally, we search for correlations between $f$ and other AGN and BLR parameters and find marginal evidence that $f$ is correlated with $M_{\rm BH}$ and the BLR inclination angle, but no significant evidence of a correlation with the AGN luminosity or Eddington ratio., Comment: 26 pages, 14 figures. Accepted for publication in ApJ

Triangulum (M33) is the most massive satellite galaxy of Andromeda (M31), with a stellar mass of about 3 × 109 M⊙. Based on abundance matching techniques, M33’s total mass at infall is estimated to be of order 1011M⊙. ΛCDM simulations predict that M33-mass halos host several of their own low-mass satellite companions, yet only one candidate M33 satellite has been detected in deep photometric surveys to date. This ‘satellites of satellites’ hierarchy has recently been explored in the context of the dwarf galaxies discovered around the Milky Way’s Magellanic Clouds in the Dark Energy Survey. Here, we discuss the number of satellite galaxies predicted to reside within the virial radius (∼160 kpc) of M33 based on ΛCDM simulations. We also calculate the expected number of satellite detections in N fields of data using various ground-based imagers. Finally, we discuss how these satellite population predictions change as a function of M33’s past orbital history. If M33 is on its first infall into M31’s halo, its proposed satellites are expected to remain bound to M33 today. However, if M33 experienced a recent tidal interaction with M31, the number of surviving satellites depends strongly on the distance achieved at pericenter due to the effects of tidal stripping. We conclude that a survey extending to ∼100 kpc around M33 would be sufficient to constrain its orbital history and a majority of its satellite population. In the era of WFIRST, surveys of this size will be considered small observing programs.

It was recently proposed that the globular cluster system of the very low surface-brightness galaxy NGC1052-DF2 is dynamically very cold, leading to the conclusion that this dwarf galaxy has little or no dark matter. Here, we show that a robust statistical measure of the velocity dispersion of the tracer globular clusters implies a mundane velocity dispersion and a poorly constrained mass-to-light ratio. Models that include the possibility that some of the tracers are field contaminants do not yield a more constraining inference. We derive only a weak constraint on the mass-to-light ratio of the system within the half-light radius (M/L_V, 5 pages, 5 figures. ApJL, in press. v2: small changes to the text and slightly more detailed analysis; conclusions unchanged

The Seyfert 1 galaxy Arp 151 was monitored as part of three reverberation mapping campaigns spanning $2008-2015$. We present modeling of these velocity-resolved reverberation mapping datasets using a geometric and dynamical model for the broad line region (BLR). By modeling each of the three datasets independently, we infer the evolution of the BLR structure in Arp 151 over a total of seven years and constrain the systematic uncertainties in non-varying parameters such as the black hole mass. We find that the BLR geometry of a thick disk viewed close to face-on is stable over this time, although the size of the BLR grows by a factor of $\sim 2$. The dynamics of the BLR are dominated by inflow and the inferred black hole mass is consistent for the three datasets, despite the increase in BLR size. Combining the inference for the three datasets yields a black hole mass and statistical uncertainty of $\log_{10}($M$_{\rm BH}/\rm{M}_{\odot})=6.82^{+0.09}_{-0.09}$ with a standard deviation in individual measurements of 0.13 dex., Comment: 21 pages, 8 figures, 2 tables. Accepted for publication in ApJ

We present the first proper motion measurement for an ultra-faint dwarf spheroidal galaxy, Segue 1, using SDSS and LBC data as the first and second epochs separated by a baseline of $\sim 10$ years. We obtain a motion of $\mu_{\alpha}\,\cos(\delta) = -0.37\pm0.57$ mas yr$^{-1}$ and $\mu_{\delta} =-3.39\pm0.58$ mas yr$^{-1}$. Combining this with the known line-of-sight velocity, this corresponds to a Galactocentric V$_\mathrm{rad}=84\pm9$ and V$_\mathrm{tan}=164^{+66}_{-55}$ km s$^{-1}$. Applying Milky Way halo masses between 0.8 to 1.6$\times 10^{12}$ M$_\odot$ results in an apocenter at 33.9$^{+21.7}_{-7.4}$ kpc and pericenter at 15.4$^{+10.1}_{-9.0}$ kpc from the Galactic center, indicating Segue~1 is rather tightly bound to the Milky Way. Since neither the orbital pole of Segue 1 nor its distance to the Milky Way is similar to the more massive classical dwarfs, it is very unlikely that Segue 1 was once a satellite of a massive known galaxy. Using cosmological zoom-in simulations of Milky Way-mass galaxies, we identify subhalos on similar orbits as Segue~1, which imply the following orbital properties: a median first infall 8.1$^{+3.6}_{-4.3}$ Gyrs ago, a median of 4 pericentric passages since then and a pericenter of 22.8$^{+4.7}_{-4.8}$ kpc. This is slightly larger than the pericenter derived directly from Segue 1 and Milky Way parameters, because galaxies with a small pericenter are more likely to be destroyed. Of the surviving subhalo analogs only 27\% were previously a satellite of a more massive dwarf galaxy (that is now destroyed), thus Segue 1 is more likely to have been accreted on its own., Comment: 16 pages, 7 figures, accepted by ApJ

We present the velocity dispersion of red giant branch (RGB) stars in M31's halo, derived by modeling the line of sight velocity distribution of over 5000 stars in 50 fields spread throughout M31's stellar halo. The dataset was obtained as part of the SPLASH (Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo) Survey, and covers projected radii of 9 to 175 kpc from M31's center. All major structural components along the line of sight in both the Milky Way (MW) and M31 are incorporated in a Gaussian Mixture Model, including all previously identified M31 tidal debris features in the observed fields. The probability an individual star is a constituent of M31 or the MW, based on a set of empirical photometric and spectroscopic diagnostics, is included as a prior probability in the mixture model. The velocity dispersion of stars in M31's halo is found to decrease only mildly with projected radius, from 108 km/s in the innermost radial bin (8.2 to 14.1 kpc) to $\sim 80$ to 90 km/s at projected radii of $\sim 40$ to 130 kpc, and can be parameterized with a power-law of slope $-0.12\pm 0.05$. The quoted uncertainty on the power-law slope reflects only the precision of the method, although other sources of uncertainty we consider contribute negligibly to the overall error budget., Submitted to the Astrophysical Journal

We present an approach for comparing the detections and non-detections of Local Group (LG) dwarf galaxies in large HI surveys to the predictions of a suite of n-body simulations of the LG. This approach depends primarily on a set of empirical scaling relations to connect the simulations to the observations, rather than making strong theoretical assumptions. We then apply this methodology to the Galactic Arecibo L-band Feed Array HI Compact Cloud Catalog (GALFA-HI CCC), and compare it to the ELVIS suite of simulations. This approach reveals a strong tension between the na\"ive results of the model and the observations: while there are no LG dwarfs in the GALFA-HI CCC, the simulations predict $\sim 10$. Applying a simple model of reionization can resolve this tension by preventing low-mass halos from forming gas. However, and if this effect operates as expected, the observations provide a constraint on the mass scale of dwarf galaxy that reionization impacts. Combined with the observed properties of Leo T, the halo virial mass scale at which reionization impacts dwarf galaxy gas content is constrained to be $\sim 10^{8.5} M_\odot$, independent of any assumptions about star formation., Comment: 10 pages, 7 figures, accepted to ApJ

astroquery is a collection of tools for requesting data from databases hosted on remote servers with interfaces exposed on the internet, including those with web pages but without formal application program interfaces (APIs). These tools are built on the Python requests package, which is used to make HTTP requests, and astropy, which provides most of the data parsing functionality. astroquery modules generally attempt to replicate the web page interface provided by a given service as closely as possible, making the transition from browser-based to command-line interaction easy. astroquery has received significant contributions from throughout the astronomical community, including several significant contributions from telescope archives. astroquery enables the creation of fully reproducible workflows from data acquisition through publication. This paper describes the philosophy, basic structure, and development model of the astroquery package. The complete documentation for astroquery can be found at http://astroquery.readthedocs.io/., Comment: Accepted to AJ. The documentation is at http://astroquery.readthedocs.io/ and the repository is at https://github.com/astropy/astroquery/

The ultra-faint satellite galaxy Hercules has a strongly elongated and irregular morphology with detections of tidal features up to 1.3 deg (3 kpc) from its center. This suggests that Hercules may be dissolving under the Milky Way's gravitational influence, and hence could be a tidal stream in formation rather than a bound, dark-matter dominated satellite. Using Bayesian inference in combination with N-body simulations, we show that Hercules has to be on a very eccentric orbit (epsilon~0.95) within the Milky Way in this scenario. On such an orbit, Hercules "explodes" as a consequence of the last tidal shock at pericenter 0.5 Gyr ago. It is currently decelerating towards apocenter of its orbit with a velocity of V=157 km/s -- of which 99% is directed radially outwards. Due to differential orbital precession caused by the non-spherical nature of the Galactic potential, its debris fans out nearly perpendicular to its orbit. This explains why Hercules has an elongated shape without showing a distance gradient along its main body: it is in fact a stream that is significantly broader than it is long. In other words, it is moving perpendicular to its apparent major axis. In this scenario, there is a spike in the radial velocity profile created by the dominant debris component that formed through the last pericenter passage. This is similar to kinematic substructure that is observed in the real Hercules. Modeling a satellite on such a highly eccentric orbit is strongly dependent on the form of the Galactic potential. We therefore propose that detailed kinematic investigation of Hercules and other exploding satellite candidates can yield strong constraints on the potential of the Milky Way., 17 pages, 12 figures, submitted to AAS, comments welcome

The Large Synoptic Survey Telescope (LSST) will be an 8.4m optical survey telescope sited in Chile and capable of imaging the entire sky twice a week. The data rate of approximately 15TB per night and the requirements to both issue alerts on transient sources within 60 seconds of observing and create annual data releases means that automated data management systems and data processing pipelines are a key deliverable of the LSST construction project. The LSST data management software has been in development since 2004 and is based on a C++ core with a Python control layer. The software consists of nearly a quarter of a million lines of code covering the system from fundamental WCS and table libraries to pipeline environments and distributed process execution. The Astropy project began in 2011 as an attempt to bring together disparate open source Python projects and build a core standard infrastructure that can be used and built upon by the astronomy community. This project has been phenomenally successful in the years since it has begun and has grown to be the de facto standard for Python software in astronomy. Astropy brings with it considerable expectations from the community on how astronomy Python software should be developed and it is clear that by the time LSST is fully operational in the 2020s many of the prospective users of the LSST software stack will expect it to be fully interoperable with Astropy. In this paper we describe the overlap between the LSST science pipeline software and Astropy software and investigate areas where the LSST software provides new functionality. We also discuss the possibilities of re-engineering the LSST science pipeline software to build upon Astropy, including the option of contributing affliated packages.

We present the first stable release of Halotools (v0.2), a community-driven Python package designed to build and test models of the galaxy-halo connection. Halotools provides a modular platform for creating mock universes of galaxies starting from a catalog of dark matter halos obtained from a cosmological simulation. The package supports many of the common forms used to describe galaxy-halo models: the halo occupation distribution (HOD), the conditional luminosity function (CLF), abundance matching, and alternatives to these models that include effects such as environmental quenching or variable galaxy assembly bias. Satellite galaxies can be modeled to live in subhalos, or to follow custom number density profiles within their halos, including spatial and/or velocity bias with respect to the dark matter profile. The package has an optimized toolkit to make mock observations on a synthetic galaxy population, including galaxy clustering, galaxy-galaxy lensing, galaxy group identification, RSD multipoles, void statistics, pairwise velocities and others, allowing direct comparison to observations. Halotools is object-oriented, enabling complex models to be built from a set of simple, interchangeable components, including those of your own creation. Halotools has an automated testing suite and is exhaustively documented on http://halotools.readthedocs.io, which includes quickstart guides, source code notes and a large collection of tutorials. The documentation is effectively an online textbook on how to build and study empirical models of galaxy formation with Python., Revisions match version accepted for publication in AAS

The Andromeda galaxy (M31) shows many tidal features in its halo, including the Giant Southern Stream (GSS) and a sharp ledge in surface density on its western side (the W Shelf). Using DEIMOS on the Keck telescope, we obtain radial velocities of M31's giant stars along its NW minor axis, in a radial range covering the W Shelf and extending beyond its edge. In the space of velocity versus radius, the sample shows the wedge pattern expected from a radial shell, which is detected clearly here for the first time. This confirms predictions from an earlier model of formation of the GSS, which proposed that the W Shelf is a shell from the third orbital wrap of the same tidal debris stream that produces the GSS, with the main body of the progenitor lying in the second wrap. We calculate the distortions in the shelf wedge pattern expected from its outward expansion and angular momentum, and show that these effects are echoed in the data. In addition, a hot, relatively smooth spheroid population is clearly present. We construct a bulge-disk-halo N-body model that agrees with surface brightness and kinematic constraints, and combine it with a simulation of the GSS. From the contrasting kinematic signatures of the hot spheroid and shelf components, we decompose the observed stellar metallicity distribution into contributions from each component using a non-parametric mixture model. The shelf component's metallicity distribution matches previous observations of the GSS superbly, further strengthening the evidence they are connected and bolstering the case for a massive progenitor of this stream.

We present astroplan - an open source, open development, Astropy affiliated package for ground-based observation planning and scheduling in Python. astroplan is designed to provide efficient access to common observational quantities such as celestial rise, set, and meridian transit times and simple transformations from sky coordinates to altitude-azimuth coordinates without requiring a detailed understanding of astropy's implementation of coordinate systems. astroplan provides convenience functions to generate common observational plots such as airmass and parallactic angle as a function of time, along with basic sky (finder) charts. Users can determine whether or not a target is observable given a variety of observing constraints, such as airmass limits, time ranges, Moon illumination/separation ranges, and more. A selection of observation schedulers are included which divide observing time among a list of targets, given observing constraints on those targets. Contributions to the source code from the community are welcome., Comment: Accepted to AJ, source code available at https://github.com/astropy/astroplan, replaced to correct typo in abstract

In the Local Group, nearly all of the dwarf galaxies (M_star < 10^9 M_sun) that are satellites within 300 kpc (the virial radius) of the Milky Way (MW) and Andromeda (M31) have quiescent star formation and little-to-no cold gas. This contrasts strongly with comparatively isolated dwarf galaxies, which are almost all actively star-forming and gas-rich. This near dichotomy implies a rapid transformation of satellite dwarf galaxies after falling into the halos of the MW or M31. We combine the observed quiescent fractions for satellites of the MW and M31 with the infall times of satellites from the Exploring the Local Volume in Simulations (ELVIS) suite of cosmological zoom-in simulations to determine the typical timescales over which environmental processes within the MW/M31 halos remove gas and quench star formation in low-mass satellite galaxies. The quenching timescales for satellites with M_star < 10^8 M_sun are short, < 2 Gyr, and quenching is more rapid at lower M_star. These satellite quenching timescales can be 1 - 2 Gyr longer if one includes the time that satellites were environmentally preprocessed by low-mass groups prior to MW/M31 infall. We compare with quenching timescales for more massive satellites from previous works to synthesize the nature of satellite galaxy quenching across the observable range of M_star = 10^{3-11} M_sun. The satellite quenching timescale increases rapidly with satellite M_star, peaking at ~9.5 Gyr for M_star ~ 10^9 M_sun, and the timescale rapidly decreases at higher M_star to < 5 Gyr at M_star > 5 x 10^9 M_sun. Overall, galaxies with M_star ~ 10^9 M_sun, similar to the Magellanic Clouds, exhibit the longest quenching timescales, regardless of environmental or internal mechanisms., 6 pages, 3 figures. Accepted in ApJ Letters. Matches published version

Initial release.

Andromeda XXVII is a dwarf spheroidal galaxy in the outskirts of the Andromeda galaxy (M31). It appears to be dissolving in to the Northern arc of M31, and could be the remnant of a strong tidal disruption. In the upcoming months, our spectroscopic program, which has measured velocities for multiple stars within both the dwarf galaxy progenitor and its stream (using the Keck II DEIMOS telescope, as part of the PAndAS survey), will determine velocity dispersions, scale radii and metallicities of both the dwarf and the stream. This in turn may enable us to ascertain the progenitor mass profile and determine whether it is cusped or cored.

Substructure in ΛCDM provides a number of interesting puzzles. While the missing satellites problem is well-studied, there are suggestions of an opposite problem on the bright end. Subhalos large enough to host luminous satellites are uncommon, so the existence of the Large Magellanic Cloud (LMC) orbiting the Galaxy can potentially be a challenge for ΛCDM. Hence, we describe a search for analogs to an isolated galaxy pair like the Milky Way/LMC system in the SDSS and interpret these results with cosmological simulations. We note that while the LMC may not be unusual based on its luminosity, it is remarkably blue for such satellites. Thus, color may have implications for the LMC’s orbital history.

Supernovae provide valuable opportunities to study galactic processes from the local Universe to large distances, but their properties and the sensitivities of current telescopes make the detection of high-redshift examples extremely difficult. Previous searches have revealed core-collapse (type II) supernovae to z ≈ 0.7 and thermonuclear (type Ia) to z ≈1.5. Now by exploiting the exceptional properties of sub-class type IIn core-collapse supernovae — including extreme brightness in the ultraviolet and bright, long-lived emission lines — Cooke et al. report the discovery in archival data of three previously unknown supernovae at redshifts z = 0.808, 2.013 and 2.357. The study of objects with redshifts z > 2 provides a window on the Universe at a time shortly after the formation of the first stars. Type IIn supernovae are luminous core-collapse explosions of massive stars that, unlike other types, are very bright in the ultraviolet and have strong, long-lived emission lines that should enable detection at redshift z ≈ 2. Here, three spectroscopically confirmed type IIn supernovae are reported at redshifts z = 0.808, 2.013 and 2.357, detected in archival data. Supernovae have been confirmed to redshift z ≈ 1.7 (refs 1, 2) for type Ia (thermonuclear detonation of a white dwarf) and to z ≈ 0.7 (refs 1, 3–5) for type II (collapse of the core of the star). The subclass type IIn (ref. 6) supernovae are luminous7,8,9 core-collapse explosions of massive stars8,9,10,11 and, unlike other types, are very bright in the ultraviolet12,13,14,15, which should enable them to be found optically at redshifts z ≈ 2 and higher14,16. In addition, the interaction of the ejecta with circumstellar material creates strong, long-lived emission lines that allow spectroscopic confirmation of many events of this type at z ≈ 2 for 3–5 years after explosion (ref. 14). Here we report three spectroscopically confirmed type IIn supernovae, at redshifts z = 0.808, 2.013 and 2.357, detected in archival data using a method14 designed to exploit these properties at z ≈ 2. Type IIn supernovae directly probe the formation of massive stars at high redshift. The number found to date is consistent with the expectations of a locally measured17 stellar initial mass function, but not with an evolving initial mass function proposed18,19,20 to explain independent observations at low and high redshift.

We present the metallicity distribution of red giant branch (RGB) stars in M31's stellar halo, derived from photometric metallicity estimates for over 1500 spectroscopically confirmed RGB halo stars. The stellar sample comes from 38 halo fields observed with the Keck/DEIMOS spectrograph, ranging from 9 to 175 kpc in projected distance from M31's center, and includes 52 confirmed M31 halo stars beyond 100 kpc. While a wide range of metallicities is seen throughout the halo, the metal-rich peak of the metallicity distribution function becomes significantly less prominent with increasing radius. The metallicity profile of M31's stellar halo shows a continuous gradient from 9 to ~100 kpc, with a magnitude of -0.01 dex/kpc. The stellar velocity distributions in each field are used to identify stars that are likely associated with tidal debris features. The removal of tidal debris features does not significantly alter the metallicity gradient in M31's halo: a gradient is maintained in fields spanning 10 to 90 kpc. We analyze the halo metallicity profile, as well as the relative metallicities of stars associated with tidal debris features and the underlying halo population, in the context of current simulations of stellar halo formation. We argue that the large scale gradient in M31's halo implies M31 accreted at least one relatively massive progenitor in the past, while the field to field variation seen in the metallicity profile indicates that multiple smaller progenitors are likely to have contributed substantially to M31's outer halo., Comment: Accepted for publication in the Astrophysical Journal. 21 pages, 16 figures

We present Keck/DEIMOS spectroscopy of resolved stars in the M31 satellites And XXVIII & And XXIX. We show that these are likely self-bound galaxies based on 18 and 24 members in And XXVIII & And XXIX, respectively. And XXVIII has a systemic velocity of -331.1 +/- 1.8 km/s and velocity dispersion of 4.9+/-1.6 km/s, implying a mass-to-light ratio (within r_1/2) of ~ 44 +/- 41. And XXIX has a systemic velocity of -194.4 +/- 1.5 km/s and velocity dispersion of 5.7+/-1.2 km/s, implying a mass-to-light ratio (within r_1/2) of ~ 124 +/- 72. The internal kinematics and implied masses of And XXVIII & And XXIX are similar to dwarf spheroidals (dSphs) of comparable luminosities, implying that these objects are dark matter-dominated dwarf galaxies. Despite the large projected distances from their host (380 and 188 kpc), the kinematics of these dSph suggest that they are bound M31 satellites., 9 pages, 5 figures, ApJ accepted

The prominent broad Fe II emission blends in the spectra of active galactic nuclei have been shown to vary in response to continuum variations, but past attempts to measure the reverberation lag time of the optical Fe II lines have met with only limited success. Here we report the detection of Fe II reverberation in two Seyfert 1 galaxies, NGC 4593 and Mrk 1511, based on data from a program carried out at Lick Observatory in Spring 2011. Light curves for emission lines including H-beta and Fe II were measured by applying a fitting routine to decompose the spectra into several continuum and emission-line components, and we use cross-correlation techniques to determine the reverberation lags of the emission lines relative to V-band light curves. In both cases the measured lag (t_cen) of Fe II is longer than that of H-beta, although the inferred lags are somewhat sensitive to the choice of Fe II template used in the fit. For spectral decompositions done using the Fe II template of Veron-Cetty et al. (2004), we find t_cen(Fe II)/t_cen(H-beta) = 1.9+-0.6 in NGC 4593 and 1.5+-0.3 in Mrk 1511. The detection of highly correlated variations between Fe II and continuum emission demonstrates that the Fe II emission in these galaxies originates in photoionized gas, located predominantly in the outer portion of the broad-line region., Comment: 14 pages, 6 figures. Accepted for publication in ApJ

We spectroscopically identify a sample of carbon stars in the satellites and halo of M31 using moderate-resolution optical spectroscopy from the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo survey. We present the photometric properties of our sample of 41 stars, including their brightness with respect to the tip of the red giant branch (TRGB) and their distributions in various color-color spaces. This analysis reveals a bluer population of carbon stars fainter than the TRGB and a redder population of carbon stars brighter than the TRGB. We then apply principal component analysis to determine the sample's eigenspectra and eigencoefficients. Correlating the eigencoefficients with various observable properties reveals the spectral features that trace effective temperature and metallicity. Putting the spectroscopic and photometric information together, we find the carbon stars in the satellites and halo of M31 to be minimally impacted by dust and internal dynamics. We also find that while there is evidence to suggest that the sub-TRGB stars are extrinsic in origin, it is also possible that they are are particularly faint members of the asymptotic giant branch., Comment: In print by ApJ

We present the surface brightness profile of M31's stellar halo out to a projected radius of 175 kpc. The surface brightness estimates are based on confirmed samples of M31 red giant branch stars derived from Keck/DEIMOS spectroscopic observations. A set of empirical spectroscopic and photometric M31 membership diagnostics is used to identify and reject foreground and background contaminants. This enables us to trace the stellar halo of M31 to larger projected distances and fainter surface brightnesses than previous photometric studies. The surface brightness profile of M31's halo follows a power-law with index -2.2 +/- 0.2 and extends to a projected distance of at least ~175 kpc (~ 2/3 of M31's virial radius), with no evidence of a downward break at large radii. The best-fit elliptical isophotes have b/a=0.94 with the major axis of the halo aligned along the minor axis of M31's disk, consistent with a prolate halo, although the data are also consistent with M31's halo having spherical symmetry. The fact that tidal debris features are kinematically cold is used to identify substructure in the spectroscopic fields out to projected radii of 90 kpc, and investigate the effect of this substructure on the surface brightness profile. The scatter in the surface brightness profile is reduced when kinematically identified tidal debris features in M31 are statistically subtracted; the remaining profile indicates a comparatively diffuse stellar component to M31's stellar halo exists to large distances. Beyond 90 kpc, kinematically cold tidal debris features can not be identified due to small number statistics; nevertheless, the significant field-to-field variation in surface brightness beyond 90 kpc suggests that the outermost region of M31's halo is also comprised to a significant degree of stars stripped from accreted objects., Comment: Accepted for publication in ApJ; v2 matches published version. Only minor editorial changes made

We present kinematical profiles and metallicity for the M31 dwarf spheroidal (dSph) satellite galaxy Andromeda II (And II) based on Keck DEIMOS spectroscopy of 531 red giant branch stars. Our kinematical sample is among the largest for any M31 satellite and extends out to two effective radii (r_eff = 5.3' = 1.1 kpc). We find a mean systemic velocity of -192.4+-0.5 km/s and an average velocity dispersion of sigma_v = 7.8+-1.1 km/s. While the rotation velocity along the major axis of And II is nearly zero (, 14 pages, 10 figures, 4 tables, accepted for publication in ApJ