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Register a new userCharacterizing the Circumgalactic Medium of the Lowest-Mass Galaxies: A Case Study of IC 1613
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Using 10 sightlines observed with the Hubble Space Telescope/Cosmic Origins Spectrograph, we study the circumgalactic medium (CGM) and outflows of IC1613, which is a low-mass ($M_*sim10^8~M_odot$), dwarf irregular galaxy on the outskirts of the Local Group. Among the sightlines, 4 are pointed towards UV-bright stars in IC1613, and the other 6 sightlines are background QSOs at impact parameters from 6 kpc ($<0.1R_{200}$) to 61 kpc ($0.6R_{200}$). We detect a number of Si II, Si III, Si IV, C II, and C IV absorbers, most of which have velocities less than the escape velocity of IC1613 and thus are gravitationally bound. The line strengths of these ion absorbers are consistent with the CGM absorbers detected in dwarf galaxies at low redshifts. Assuming that Si II, Si III, and Si IV comprise nearly 100% of the total silicon, we find 3% ($sim$8$times$10$^3~{rm M_odot}$), 2% ($sim$7$times$10$^3~{rm M_odot}$), and 32--42% [$sim$(1.0--1.3)$times$10$^5~{rm M_odot}$] of the silicon mass in the stars, interstellar medium, and within $0.6R_{200}$ of the CGM of IC1613. We also estimate the metal outflow rate to be ${rm dot{M}_{out, Z}geq1.1times10^{-5}~M_odot~yr^{-1}}$ and the instantaneous metal mass loading factor to be $eta_{rm Z}geq0.004$, which are in broad agreement with available observation and simulation values. This work is the first time a dwarf galaxy of such low mass is probed by a number of both QSO and stellar sightlines, and it shows that the CGM of low-mass gas-rich galaxies can be a large reservoir enriched with metals from past and ongoing outflows.
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We report a definitive detection of chemically-enriched cool gas around massive, quiescent galaxies at z~0.4-0.7. The result is based on a survey of 37621 luminous red galaxy (LRG)-QSO pairs in SDSS DR12 with projected distance d<500 kpc. The LRGs are characterized by a predominantly old (age>~1Gyr) stellar population with 13% displaying [OII] emission features and LINER-like spectra. Both passive and [OII]-emitting LRGs share the same stellar mass distribution with a mean of <log(M*/Msun)>~11.4 and a dispersion of 0.2 dex. Both LRG populations exhibit associated strong MgII absorbers out to d<500 kpc. The mean gas covering fraction at d<~120 kpc is <kappa>_MgII > 15% and declines quickly to <kappa>_MgII ~ 5% at d<~500 kpc. No clear dependence on stellar mass is detected for the observed MgII absorption properties. The observed velocity dispersion of MgII absorbing gas relative to either passive or [OII]-emitting LRGs is merely 60% of what is expected from virial motion in these massive halos. While no apparent azimuthal dependence is seen for <kappa>_MgII around passive LRGs at all radii, a modest enhancement in <kappa>_MgII is detected along the major axis of [OII]-emitting LRGs at d<50 kpc. The suppressed velocity dispersion of MgII absorbing gas around both passive and [OII]-emitting LRGs, together with an elevated <kappa>_MgII along the major axis of [OII]-emitting LRGs at d<50 kpc, provides important insights into the origin of the observed chemically-enriched cool gas in LRG halos. We consider different scenarios and conclude that the observed MgII absorbers around LRGs are best-explained by a combination of cool clouds formed in thermally unstable LRG halos and satellite accretion through filaments.
We present the first characterization of the diffuse gas and metals in the circumgalactic medium of 96 z = 2.9-3.8 Ly$alpha$ emitters (LAEs) detected with the Multi-Unit Spectroscopic Explorer (MUSE) in fields centered on 8 bright background quasars as part of our MUSEQuBES survey. The LAEs have relatively low Ly$alpha$ luminosities (~$10^{42}$ erg/s) and star formation rates ~1 $M_odot$/yr, which for main sequence galaxies corresponds to stellar masses of only ~$10^{8.6}$ $M_{odot}$. The median transverse distance between the LAEs and the quasar sightlines is 165 proper kpc (pkpc). We stacked the high-resolution quasar spectra and measured significant excess HI and CIV absorption near the LAEs out to 500 km/s and at least 250 pkpc (corresponding to ~7 virial radii). At < 30 km/s from the galaxies the median HI and CIV optical depths are enhanced by an order of magnitude. The average rest-frame equivalent width of Ly$alpha$ absorption is comparable to that for Lyman-break galaxies (LBGs) at z~2.3 and ~L* galaxies at z~0.2, but considerably higher than for sub-L*/dwarf galaxies at low redshift. The CIV equivalent width is comparable to those measured for low-z dwarf galaxies and z~2.3 LBGs but significantly lower than for z~2.3 quasar-host galaxies. The absorption is significantly stronger around the ~ 1/3 of our LAEs that are part of groups, which we attribute to the large-scale structures in which they are embedded. We do not detect any strong dependence of either the HI or CIV absorption on transverse distance (over the range 50-250 pkpc), redshift, or the properties of the Ly$alpha$ emission line (luminosity, full width at half maximum, or equivalent width). However, for HI, but not CIV, the absorption at < 100 km/s from the LAE does increase with the star formation rate. This suggests that LAEs surrounded by more neutral gas tend to have higher star formation rates.
In order to study the circumgalactic medium (CGM) of galaxies we develop an automated pipeline to estimate the optical continuum of quasars and detect intervening metal absorption line systems with a matched kernel convolution technique and adaptive S/N criteria. We process $sim$ one million quasars in the latest Data Release 16 (DR16) of the Sloan Digital Sky Survey (SDSS) and compile a large sample of $sim$ 160,000 MgII absorbers, together with $sim$ 70,000 FeII systems, in the redshift range $0.35<z_{abs}<2.3$. Combining these with the SDSS DR16 spectroscopy of $sim1.1$ million luminous red galaxies (LRGs) and $sim 200,000$ emission line galaxies (ELGs), we investigate the nature of cold gas absorption at $0.5<z<1$. These large samples allow us to characterize the scale dependence of MgII with greater accuracy than in previous work. We find that there is a strong enhancement of MgII absorption within $sim 50$ kpc of ELGs, and the covering fraction within $0.5r_{rm vir}$ of ELGs is 2-5 times higher than for LRGs. Beyond 50 kpc, there is a sharp decline in MgII for both kinds of galaxies, indicating a transition to the regime where the CGM is tightly linked with the dark matter halo. The MgII covering fraction correlates strongly with stellar mass for LRGs, but weakly for ELGs, where covering fractions increase with star formation rate. Our analysis implies that cool circumgalactic gas has a different physical origin for star forming versus quiescent galaxies.
IC 1613 is a Local Group dwarf irregular galaxy at a distance of 750 kpc. In this work, we present an analysis of the star formation history (SFH) of a field of $sim200$ square arcmin in the central part of the galaxy. To this aim, we use a novel method based on the resolved population of more highly evolved stars. We identify 53 such stars, 8 of which are supergiants and the remainder are long period variables (LPV), large amplitude variables (LAV) or extreme Asymptotic Giant Branch (x-AGB) stars. Using stellar evolution models, we find the age and birth mass of these stars and thus reconstruct the SFH. The average rate of star formation during the last Gyr is $sim3times10^{-4}$ M$_odot$ yr$^{-1}$ kpc$^{-2}$. The absence of a dominant epoch of star formation over the past 5 Gyr, suggests that IC 1613 has evolved in isolation for that long, spared harrassment by other Local Group galaxies (in particular M 31 and the Milky Way). We confirm the radial age gradient, with star formation currently concentrated in the central regions of IC 1613, and the failure of recent star formation to have created the main HI supershell. Based on the current rate of star formation at $(5.5pm2)times10^{-3}$ M$_odot$ yr$^{-1}$, the interstellar gas mass of the galaxy of $9times10^7$ M$_odot$ and the gas production rate from AGB stars at $sim6times10^{-4}$ M$_odot$ yr$^{-1}$, we conclude that the star formation activity of IC 1613 can continue for $sim18$ Gyr in a closed-box model, but is likely to cease much earlier than that unless gas can be accreted from outside.
The circumgalactic medium (CGM), which harbors > 50% of all the baryons in a galaxy, is both the reservoir of gas for subsequent star formation and the depository of chemically processed gas, energy, and angular momentum from feedback. As such, the CGM obviously plays a critical role in galaxy evolution. We discuss the opportunity to image this component using recombination line emission, beginning with the early results coming from recent statistical detection of this emission to the final goal of realizing spectral-line images of the CGM in individual nearby galaxies. Such work will happen in the next decade and provide new insights on the galactic baryon cycle.
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