arXiv subjects

Christopher W. Churchill

Publications and source records attributed to Christopher W. Churchill.

At least 55 records · Page 3Linked to original sources

arXiv2016

MAGIICAT IV. Kinematics of the Circumgalactic Medium and Evidence for Quiescent Evolution Around Red Galaxies

The equivalent widths of MgII absorption in the circumgalactic medium (CGM) trace the global star formation rate up to $z<6$, are larger for star-forming galaxies than passively-evolving galaxies, and decrease with increasing distance from the galaxy. We delve further into the physics involved by investigating gas kinematics and cloud column density distributions as a function of galaxy color, redshift, and projected distance from the galaxy (normalized by galaxy virial radius, $D/R_{\rm vir}$). For 39 isolated galaxies at $0.3<z_{\rm gal}<1.0$, we have detected MgII absorption in high-resolution ($Δv\simeq 6.6$ km/s) spectra of background quasars within a projected distance of $7<D<190$ kpc. We characterize the absorption velocity spread using pixel-velocity two-point correlation functions. Velocity dispersions and cloud column densities for blue galaxies do not differ with redshift nor with $D/R_{\rm vir}$. This suggests that outflows continually replenish the CGM of blue galaxies with high velocity dispersion, large column density gas out to large distances. Conversely, absorption hosted by red galaxies evolves with redshift where the velocity dispersions (column densities) are smaller (larger) at $z_{\rm gal}<0.656$. After taking into account larger possible velocities in more massive galaxies, we find that there is no difference in the velocity dispersions or column densities for absorption hosted by red galaxies with $D/R_{\rm vir}$. Thus, a lack of outflows in red galaxies causes the CGM to become more quiescent over time, with lower velocity dispersions and larger column densities towards lower $z_{\rm gal}$. The quenching of star formation appears to affect the CGM out to $D/R_{\rm vir}=0.75$.

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arXiv2015

The Azimuthal Dependence of Outflows and Accretion Detected Using OVI Absorption

We report a bimodality in the azimuthal angle ($Φ$) distribution of gas around galaxies traced by OVI absorption. We present the mean $Φ$ probability distribution function of 29 HST-imaged OVI absorbing (EW>0.1A) and 24~non-absorbing (EW<0.1A) isolated galaxies (0.08<z<0.67) within 200kpc of background quasars. We show that EW is anti-correlated with impact parameter and OVI covering fraction decreases from 80% within 50kpc to 33% at 200kpc. The presence of OVI absorption is azimuthally dependent and occurs between $\pm10-20^{\circ}$ of the galaxy projected major axis and within $\pm30^{\circ}$ of the projected minor axis. We find higher EWs along the projected minor axis with weaker EWs along the project major axis. Highly inclined galaxies have the lowest covering fractions due to minimized outflow/inflow cross-section geometry. Absorbing galaxies also have bluer colors while non-absorbers have redder colors, suggesting that star-formation is a key driver in the OVI detection rate. OVI surrounding blue galaxies exists primarily along the projected minor axis with wide opening angles while OVI surrounding red galaxies exists primarily along the projected major axis with smaller opening angles, which may explain why absorption around red galaxies is less frequently detected. Our results are consistent with CGM originating from major axis-fed inflows/recycled gas and from minor axis-driven outflows. Non-detected OVI occurs between $Φ=20-60^{\circ}$, suggesting that OVI is not mixed throughout the CGM and remains confined within the outflows and the disk-plane. We find low OVI covering fractions within $\pm10^{\circ}$ of the projected major axis, suggesting that cool dense gas resides in a narrow planer geometry surrounded by diffuse OVI gas.

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arXiv2015

MAGIICAT V. Orientation of Outflows and Accretion Determine the Kinematics and Column Densities of the Circumgalactic Medium

We investigate the dependence of gas kinematics and column densities in the MgII-absorbing circumgalactic medium on galaxy color, azimuthal angle, and inclination to trace baryon cycle processes. Our sample of 30 foreground isolated galaxies at $0.3<z_{\rm gal}<1.0$, imaged with the Hubble Space Telescope, are probed by background quasars within a projected distance of $20<D<110$ kpc. From the high-resolution ($Δv\simeq 6.6$ km s$^{-1}$) quasar spectra, we quantify the extent of the absorber velocity structure with pixel-velocity two-point correlation functions. Absorbers with the largest velocity dispersions are associated with blue, face-on ($i<57^{\circ}$) galaxies probed along the projected minor axis ($Φ\geq 45^{\circ}$), while those with the smallest velocity dispersions belong to red, face-on galaxies along the minor axis. The velocity structure is similar for edge-on ($i \geq 57^{\circ}$) galaxies regardless of galaxy color or azimuthal angle, for red galaxies with azimuthal angle, and for blue and red galaxies probed along the projected major axis ($Φ<45^{\circ}$). The cloud column densities for face-on galaxies and red galaxies are smaller than for edge-on galaxies and blue galaxies, respectively. These results are consistent with biconical outflows along the minor axis for star-forming galaxies and accreting and/or rotating gas, which is most easily observed in edge-on galaxies probed along the major axis. Gas entrained in outflows may be fragmented with large velocity dispersions, while gas accreting onto or rotating around galaxies may be more coherent due to large path lengths and smaller velocity dispersions. Quiescent galaxies may exhibit little-to-no outflows along the minor axis, while accretion/rotation may exist along the major axis.

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arXiv2015

An Extreme Metallicity, Large-Scale Outflow from a Star-Forming Galaxy at z ~ 0.4

We present a detailed analysis of a large-scale galactic outflow in the CGM of a massive (M_h ~ 10^12.5 Msun), star-forming (6.9 Msun/yr), sub-L* (0.5 L_B*) galaxy at z=0.39853 that exhibits a wealth of metal-line absorption in the spectra of the background quasar Q 0122-003 at an impact parameter of 163 kpc. The galaxy inclination angle (i=63 degree) and the azimuthal angle (Phi=73 degree) imply that the QSO sightline is passing through the projected minor-axis of the galaxy. The absorption system shows a multiphase, multicomponent structure with ultra-strong, wide velocity spread OVI (logN = 15.16\pm0.04, V_{90} = 419 km/s) and NV (logN = 14.69\pm0.07, V_{90} = 285 km/s) lines that are extremely rare in the literature. The highly ionized absorption components are well explained as arising in a low density (10^{-4.2} cm^{-3}), diffuse (10 kpc), cool (10^4 K) photoionized gas with a super-solar metallicity ([X/H] > 0.3). From the observed narrowness of the Lyb profile, the non-detection of SIV absorption, and the presence of strong CIV absorption we rule out equilibrium/non-equilibrium collisional ionization models. The low-ionization photoionized gas with a density of 10^{-2.5} cm^{-3} and a metallicity of [X/H] > -1.4 is possibly tracing recycled halo gas. We estimate an outflow mass of ~2x10^{10} Msun, a mass-flow rate of ~54 Msun/yr, a kinetic luminosity of ~9x10^{41} erg/s, and a mass loading factor of ~8 for the outflowing high-ionization gas. These are consistent with the properties of "down-the-barrel" outflows from infrared-luminous starbursts as studied by Rupke et al. Such powerful, large-scale, metal-rich outflows are the primary means of sufficient mechanical and chemical feedback as invoked in theoretical models of galaxy formation and evolution.

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arXiv2015

Direct Insights into Observational Absorption Line Analysis Methods of the Circumgalactic Medium Using Cosmological Simulations

We study the circumgalactic medium (CGM) of a z=0.54 simulated dwarf galaxy using hydroART simulations. We present our analysis methods, which emulate observations, including objective absorption line detection, apparent optical depth (AOD) measurements, Voigt profile (VP) decomposition, and ionization modeling. By comparing the inferred CGM gas properties from the absorption lines directly to the gas selected by low ionization HI and MgII, and by higher ionization CIV and OVI absorption, we examine how well observational analysis methods recover the "true" properties of CGM gas. In this dwarf galaxy, low ionization gas arises in sub-kiloparsec "cloud" structures, but high ionization gas arises in multiple extended structures spread over 100 kpc; due to complex velocity fields, highly separated structures give rise to absorption at similar velocities. We show that AOD and VP analysis fails to accurately characterize the spatial, kinematic, and thermal conditions of high ionization gas. We find that HI absorption selected gas and OVI absorption gas arise in totally distinct physical gas structures, calling into question current observational techniques employed to infer metallicities and the total mass of "warm-hot" CGM gas. We present a method to determine whether CIV and OVI absorbing gas is photo or collisionally ionized and whether the assumption of ionization equilibrium is sound. As we discuss, these and additional findings have strong implications for how accurately currently employed observational absorption line methods recover the true gas properties, and ultimately, our ability to understand the CGM and its role in galaxy evolution.

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arXiv2014

Probing the circumgalactic medium of active galactic nuclei with background quasars

We performed a detailed study of the extended cool gas, traced by MgII absorption [$W_r(2796)\geq0.3$~Å], surrounding 14 narrow-line active galactic nuclei (AGNs) at 0.12 50$ km/s, indicating outflowing gas. The 2/2 intrinsic MgII systems have outflow velocities a factor of $\sim4$ higher than the NaID outflow velocities. Our results are consistent with AGN-driven outflows destroying the cool gas within their halos, which dramatically decreases their cool gas covering fraction, while star-burst driven winds are expelling cool gas into their circumgalactic media (CGM). This picture appears contrary to quasar--quasar pair studies which show that the quasar CGM contains significant amounts of cool gas whereas intrinsic gas found `down-the-barrel' of quasars reveals no cool gas. We discuss how these results are complementary and provide support for the AGN unified model.

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arXiv2014

Ionization Modeling Astrophysical Gaseous Structures. I. The Optically Thin Regime

We present a code for modelling the ionization conditions of optically thin astrophysical gas structures. Given the gas hydrogen density, equilibrium temperature, elemental abundances, and the ionizing spectrum, the code solves the equilibrium ionization fractions and number densities for all ions from hydrogen to zinc. The included processes are photoionization, Auger ionization, direct collisional ionization, excitation auto-ionization, charge exchange ionization, two-body radiative recombination, dielectronic recombination, and charge exchange recombination. The ionizing spectrum can be generalized to include the ultraviolet background (UVB) and/or Starburst99 stellar populations of various masses, ages, metallicities, and distances. The ultimate goal with the code is to provide fast computation of the ionization conditions of gas in N-body + hydrodynamics cosmological simulations, in particular adaptive mesh refinement codes, in order to facilitate absorption line analysis of the simulated gas for comparison with observations. To this end, we developed a method to linearize the rate equations and efficiently solve the rate matrix with a minimum number of iterations. Comparing the code to Cloudy 13.03 (Ferland), we find that the hydrogen and helium ionization fractions and the metal species ionization corrections are in excellent agreement. We discuss the science drivers and plans for further development of the ionization code to a full radiative hydrodynamic routine that can be employed for processing the simulations. A stand-alone version of the code has been made publicly available (http://astronomy.nmsu.edu/cwc/Software/Ioncode/).

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arXiv2014

Halo Mass Dependence of HI and OVI Absorption: Evidence for Differential Kinematics

We studied a sample of 14 galaxies (0.1 < z < 0.7) using HST/WFPC2 imaging and high-resolution HST/COS or HST/STIS quasar spectroscopy of Lya, Lyb, OVI1031, and OVI1037 absorption. The galaxies, having 10.8 < log(M/M_solar) < 12.2, lie within D = 300 kpc of quasar sightlines, probing out to D/R_vir = 3. When the full range of galaxy virial masses and D/R_vir of the sample are examined, 40% of the HI absorbing clouds can be inferred to be escaping their host halo. The fraction of bound clouds decreases as D/R_vir increases such that the escaping fraction is around 15% for D/R_vir < 1, around 45% for 1 < D/R_vir < 2, and around 90% for 2 < D/R_vir < 3. Adopting the median mass log(M/M_solar) = 11.5 to divide the sample into "higher" and "lower" mass galaxies, we find mass dependency for the hot CGM kinematics. To our survey limits, OVI absorption is found in only 40% of the HI clouds in and around lower mass halos as compared to 85% around higher mass halos. For D/R < 1, lower mass halos have an escape fraction of 65%, whereas higher mass halos have an escape fraction of 5%. For 1 < D/R_vir < 2, the escape fractions are 55% and 35% for lower mass and higher mass halos, respectively. For 2 < D/R_vir < 3, the escape fraction for lower mass halos is around 90%. We show that it is highly likely that the absorbing clouds reside within 4 virial radii of their host galaxies and that the kinematics are dominated by outflows. Our finding of "differential kinematics" is consistent with the scenario of "differential wind recycling" proposed by Oppenheimer et al. We discuss the implications for galaxy evolution, the stellar to halo mass function, and the mass metallicity relationship of galaxies.

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arXiv2014

New Perspective on Galaxy Outflows From the First Detection of Both Intrinsic and Traverse Metal-Line Absorption

We present the first observation of a galaxy (z=0.2) that exhibits metal-line absorption back-illuminated by the galaxy ("down-the-barrel") and transversely by a background quasar at a projected distance of 58 kpc. Both absorption systems, traced by MgII, are blueshifted relative to the galaxy systemic velocity. The quasar sight-line, which resides almost directly along the projected minor axis of the galaxy, probes MgI and MgII absorption obtained from Keck/LRIS and Lya, SiII and SiIII absorption obtained from HST/COS. For the first time, we combine two independent models used to quantify the outflow properties for down-the-barrel and transverse absorption. We find that the modeled down-the-barrel deprojected outflow velocities range between $V_{dtb}=45-255$ km/s. The transverse bi-conical outflow model, assuming constant-velocity flows perpendicular to the disk, requires wind velocities $V_{outflow}=40-80$ km/s to reproduce the transverse MgII absorption kinematics, which is consistent with the range of $V_{dtb}$. The galaxy has a metallicity, derived from H$α$ and NII, of $[{\rm O/H}]=-0.21\pm0.08$, whereas the transverse absorption has $[{\rm X/H}]=-1.12\pm0.02$. The galaxy star-formation rate is constrained between $4.6-15$ M$_{\odot}$/yr while the estimated outflow rate ranges between $1.6-4.2$ M$_{\odot}$/yr and yields a wind loading factor ranging between $0.1-0.9$. The galaxy and gas metallicities, the galaxy-quasar sight-line geometry, and the down-the-barrel and transverse modeled outflow velocities collectively suggest that the transverse gas originates from ongoing outflowing material from the galaxy. The $\sim$1 dex decrease in metallicity from the base of the outflow to the outer halo suggests metal dilution of the gas by the time it reached 58 kpc.

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arXiv2014

Radiative feedback and the low efficiency of galaxy formation in low-mass haloes at high redshift

Any successful model of galaxy formation needs to explain the low rate of star formation in the small progenitors of today's galaxies. This inefficiency is necessary for reproducing the low stellar-to-virial mass fractions, suggested by current abundance matching models. A possible driver of this low efficiency is the radiation pressure exerted by ionizing photons from massive stars. The effect of radiation pressure in cosmological, zoom-in galaxy formation simulations is modeled as a non-thermal pressure that acts only in dense and optically thick star-forming regions. We also include photoionization and photoheating by massive stars. The full photoionization of hydrogen reduces the radiative cooling in the $10^{4-4.5}$ K regime. The main effect of radiation pressure is to regulate and limit the high values of gas density and the amount of gas available for star formation. This maintains a low star formation rate of $\sim 1 \ {\rm M_\odot} \ {\rm yr}^{-1}$ in halos with masses about $10^{11} \ {M_\odot}$ at $z\simeq3$. Infrared trapping and photoionization/photoheating processes are secondary effects in this mass range. The galaxies residing in these low-mass halos contain only $\sim0.6\%$ of the total virial mass in stars, roughly consistent with abundance matching. Radiative feedback maintains an extended galaxy with a rising circular velocity profile.

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arXiv2013

MAGIICAT III. Interpreting Self-Similarity of the Circumgalactic Medium with Virial Mass using MgII Absorption

In Churchill et al., we used halo abundance matching applied to 182 galaxies in the MgII Absorber-Galaxy Catalog (MAGIICAT, Nielsen et al.) and showed that the mean MgII 2796 equivalent width follows a tight inverse-square power law, W_r(2796) ~ (D/R_vir)^-2, with projected location relative to the galaxy virial radius and that the MgII absorption covering fraction is invariant with galaxy virial mass, M_h, over the range 10.7 < M_h/M_solar < 13.9. In this work, we explore multivariate relationships between W_r(2796), virial mass, impact parameter, virial radius, and the theoretical cooling radius that further elucidate self-similarity in the cool/warm (T=10^{4-4.5} K) circumgalactic medium (CGM) with virial mass. We show that virial mass determines the extent and strength of the MgII absorbing gas such that the mean W_r(2796) increases with virial mass at fixed distance while decreasing with galactocentric distance for fixed virial mass. The majority of the absorbing gas resides within D ~ 0.3 R_vir, independent of both virial mass and minimum absorption threshold; inside this region, and perhaps also in the region 0.3 < D/R_vir = 1, the mean W_r(2796) is independent of virial mass. Contrary to absorber-galaxy cross-correlation studies, we show there is no anti-correlation between W_r(2796) and virial mass. We discuss how simulations and theory constrained by observations fully support self-similarity of the cool/warm CGM via the physics governing star formation, gas-phase metal enrichment, recycling efficiency of galactic scale winds, filament and merger accretion, and overdensity of local environment as a function of virial mass.

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arXiv2013

The Smooth MgII gas distribution through the interstellar/extra-planar/halo interface

We report the first measurements of MgII absorption systems associated with spectroscopically confirmed z~0.1 star-forming galaxies at projected distances of D<6kpc. We demonstrate the data are consistent with the well known anti-correlation between rest-frame MgII equivalent width, Wr(2796), and impact parameter, D, represented by a single log-linear relation derived by Nielsen et al. (MAGIICAT) that converges to ~2A at D=0kpc. Incorporating MAGIICAT, we find that the halo gas covering fraction is unity below D~25kpc. We also report that our D<6kpc absorbers are consistent with the Wr(2796) distributions of the Milky Way interstellar medium (ISM) and ISM+halo. In addition, quasar sight-lines of intermediate redshift galaxies with 6<D<25kpc have an equivalent width distribution similar to that of the Milky Way halo, implying that beyond ~6kpc, quasar sight-lines are likely probing halo gas and not the ISM. As inferred by the Milky Way and our new data, the gas profiles of galaxies can be fit by a single log-linear Wr(2796)-D relation out to large scales across a variety of gas-phase conditions and is maintained through the halo/extra-planar/ISM interfaces, which is remarkable considering their kinematic complexity. These low redshift, small impact parameter absorption systems are the first steps to bridge the gap between quasar absorption-line studies and HI observations of the CGM.

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arXiv2013

MAGIICAT I. The MgII Absorber-Galaxy Catalog

We describe the MgII Absorber-Galaxy Catalog, MAGIICAT, a compilation of 182 spectroscopically identified intermediate redshift (0.07 < z < 1.1) galaxies with measurements of MgII 2796, 2803 absorption from their circumgalactic medium within projected distances of 200 kpc from background quasars. In this work, we present "isolated" galaxies, which are defined as having no spectroscopically identified galaxy within a projected distance of 100 kpc and a line of sight velocity separation of 500 km/s. We standardized all galaxy properties to the Lambda CDM cosmology and galaxy luminosities, absolute magnitudes, and rest-frame colors to the B- and K-band on the AB system. We present galaxy properties and rest-frame MgII equivalent width, Wr(2796), versus galaxy redshift. The well-known anti-correlation between Wr(2796) and quasar-galaxy impact parameter, D, is significant to the 8 sigma level. The mean color of MAGIICAT galaxies is consistent with an Sbc galaxy for all redshifts. We also present B- and K-band luminosity functions for different Wr(2796) and redshift subsamples: "weak absorbing" [Wr(2796) < 0.3 Ang], "strong absorbing" [Wr(2796) > 0.3 Ang], low redshift (z < zmed), and high redshift (z > zmed), where zmed = 0.359 is the median galaxy redshift. Rest-frame color B-K correlates with M_K at the 8 sigma level for the whole sample but is driven by the strong absorbing, high redshift subsample (6 sigma). Using M_K as a proxy for stellar mass and examining the luminosity functions, we infer that in lower stellar mass galaxies, MgII absorption is preferentially detected in blue galaxies and the absorption is more likely to be weak.

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arXiv2013

MAGIICAT II. General Characteristics of the MgII Absorbing Circumgalactic Medium

We examine the MgII absorbing circumgalactic medium (CGM) for the 182 intermediate redshift (0.072 < z < 1.120) galaxies in the "MgII Absorber-Galaxy Catalog" (MAGIICAT, Nielsen et al.). We parameterize the anti-correlation between equivalent width, Wr(2796), and impact parameter, D, with a log-linear fit, and show that a power law poorly describes the data. We find that higher luminosity galaxies have larger Wr(2796) at larger D (4.3 sigma). The covering fractions, f_c, decrease with increasing D and Wr(2796) detection threshold. Higher luminosity galaxies have larger f_c; no absorption is detected in lower luminosity galaxies beyond 100 kpc. Bluer and redder galaxies have similar f_c for D < 100 kpc, but for D > 100 kpc, bluer galaxies have larger f_c, as do higher redshift galaxies. The "absorption radius", R(L)=R*(L/L*)^{beta}$, which we examine for four different Wr(2796) detection thresholds, is more luminosity sensitive to the B-band than the K-band, more sensitive for redder galaxies than for bluer galaxies, and does not evolve with redshift for the K-band, but becomes more luminosity sensitive towards lower redshift for the B-band. These trends clearly indicate a more extended MgII absorbing CGM around higher luminosity, bluer, and higher redshift galaxies. Several of our findings are in conflict with other works. We address these conflicts and discuss the implications of our results for the low-ionization, intermediate redshift CGM.

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arXiv2013

The Self-Similarity of the Circumgalactic Medium with Galaxy Virial Mass: Implications for Cold-Mode Accretion

We apply halo abundance matching to obtain galaxy virial masses, M_h, and radii, Rvir, for the 183 isolated galaxies in the "MgII Absorber-Galaxy Catalog" (MAGIICAT, Nielsen et al.). All galaxies have spectroscopic redshifts (0.1 < z < 1.1) and their circumgalactic medium (CGM) is probed in MgII absorption within projected galactocentric distances D < 200 kpc. We examine the behavior of equivalent width, W(2796), and covering fraction, f_c, as a function of D, D/Rvir, and M_h. We find: [1] systematic segregation of M_h on the W(2796)-D plane (4.0 sigma); high-mass halos are found at higher D with larger W(2796) compared to lower mass halos. On the W(2796)-D/Rvir plane, mass segregation vanishes and we find W(2796) ~ (D/Rvir)^-2 (8.9 sigma); [2] higher mass halos have larger f_c at a given D, whereas f_c is independent of M_h at all D/Rvir; [3] f_c is constant with M_h over the range 10.7 < log(M_h/Msun) < 13.8 within a given D or D/Rvir. The combined results suggest that the MgII absorbing CGM is self-similar with halo mass, even above log(M_h/Msun)~12, where cold mode accretion is theoretically predicted to be quenched. If theory is correct, either outflows or sub-halos must contribute to absorption in high-mass halos such that low- and high-mass halos are observationally indistinguishable using MgII absorption strength once impact parameter is scaled by halo mass. Alternatively, the data may indicate that predictions of a universal shut down of cold-mode accretion in high-mass halos may require revision.

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arXiv2013

The Redshift Distribution of Intervening Weak MgII Quasar Absorbers and a Curious Dependence on Quasar Luminosity

We have identified 469 MgII doublet systems having W_r >= 0.02 Å in 252 Keck/HIRES and UVES/VLT quasar spectra over the redshift range 0.1 < z < 2.6. Using the largest sample yet of 188 weak MgII systems (0.02 Å <= W_r < 0.3 Å), we calculate their absorber redshift path density, dN/dz. We find clear evidence of evolution, with dN/dz peaking at z ~ 1.2, and that the product of the absorber number density and cross section decreases linearly with increasing redshift; weak MgII absorbers seem to vanish above z ~ 2.7. If the absorbers are ionized by the UV background, we estimate number densities of 10^6 - 10^9 per Mpc^3 for spherical geometries and 10^2 - 10^5 per Mpc^3 for more sheetlike geometries. We also find that dN/dz toward intrinsically faint versus bright quasars differs significantly for weak and strong (W_r >= 1.0 Å) absorbers. For weak absorption, dN/dz toward bright quasars is ~ 25% higher than toward faint quasars (10 sigma at low redshift, 0.4 <= z <= 1.4, and 4 sigma at high redshift, 1.4 < z <= 2.34). For strong absorption the trend reverses, with dN/dz toward faint quasars being ~ 20% higher than toward bright quasars (also 10 sigma at low redshift and 4 sigma at high redshift). We explore scenarios in which beam size is proportional to quasar luminosity and varies with absorber and quasar redshifts. These do not explain dN/dz's dependence on quasar luminosity.

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arXiv2012

Discovery of Multi-Phase Cold Accretion in a Massive Galaxy at z=0.7

We present detailed photo+collisional ionization models and kinematic models of the multi-phase absorbing gas, detected within the HST/COS, HST/STIS, and Keck/HIRES spectra of the background quasar TON 153, at 104 kpc along the projected minor axis of a star-forming spiral galaxy (z=0.6610). Complementary g'r'i'Ks photometry and stellar population models indicate that the host galaxy is dominated by a 4 Gyr stellar population with slightly greater than solar metallicity and has an estimated log(M*)=11 and a log(Mvir)=13. Photoionization models of the low ionization absorption, (MgI, SiII, MgII and CIII) which trace the bulk of the hydrogen, constrain the multi-component gas to be cold (logT=3.8-5.2) and metal poor (-1.68<[X/H]<-1.64). A lagging halo model reproduces the low ionization absorption kinematics, suggesting gas coupled to the disk angular momentum, consistent with cold accretion mode material in simulations. The CIV and OVI absorption is best modeled in a separate collisionally ionized metal-poor (-2.50<[X/H]<-1.93) warm phase with logT=5.3. Although their kinematics are consistent with a wind model, given the 2-2.5dex difference between the galaxy stellar metallicity and the absorption metallicity indicates the gas cannot arise from galactic winds. We discuss and conclude that although the quasar sight-line passes along the galaxy minor axis at projected distance of 0.3 virial radii, well inside its virial shock radius, the combination of the relative kinematics, temperatures, and relative metallicities indicated that the multi-phase absorbing gas arises from cold accretion around this massive galaxy. Our results appear to contradict recent interpretations that absorption probing the projected minor axis of a galaxy is sampling winds.

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arXiv2012

Quenched Cold Accretion of a Large Scale Metal-Poor Filament due to Virial Shocking in the Halo of a Massive z=0.7 Galaxy

Using HST/COS/STIS and HIRES/Keck high-resolution spectra, we have studied a remarkable HI absorbing complex at z=0.672 toward the quasar Q1317+277. The HI absorption has a velocity spread of 1600 km/s, comprises 21 Voigt profile components, and resides at an impact parameter of D=58 kpc from a bright, high mass [log(M_vir/M_sun) ~ 13.7] elliptical galaxy that is deduced to have a 6 Gyr old, solar metallicity stellar population. Ionization models suggest the majority of the structure is cold gas surrounding a shock heated cloud that is kinematically adjacent to a multi-phase group of clouds with detected CIII, CIV and OVI absorption, suggestive of a conductive interface near the shock. The deduced metallicities are consistent with the moderate in situ enrichment relative to the levels observed in the z ~ 3 Ly-alpha forest. We interpret the HI complex as a metal-poor filamentary structure being shock heated as it accretes into the halo of the galaxy. The data support the scenario of an early formation period (z > 4) in which the galaxy was presumably fed by cold-mode gas accretion that was later quenched via virial shocking by the hot halo such that, by intermediate redshift, the cold filamentary accreting gas is continuing to be disrupted by shock heating. Thus, continued filamentary accretion is being mixed into the hot halo, indicating that the star formation of the galaxy will likely remain quenched. To date, the galaxy and the HI absorption complex provide some of the most compelling observational data supporting the theoretical picture in which accretion is virial shocked in the hot coronal halos of high mass galaxies.

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