24 research outputs found
HST Detection of Extended Neutral Hydrogen in a Massive Elliptical at z = 0.4
We report the first detection of extended neutral hydrogen (HI) gas in the
interstellar medium (ISM) of a massive elliptical galaxy beyond z~0. The
observations utilize the doubly lensed images of QSO HE 0047-1756 at z_QSO =
1.676 as absorption-line probes of the ISM in the massive (M_star ~ 10^11
M_sun) elliptical lens at z = 0.408, detecting gas at projected distances of d
= 3.3 and 4.6 kpc on opposite sides of the lens. Using the Space Telescope
Imaging Spectrograph (STIS), we obtain UV absorption spectra of the lensed QSO
and identify a prominent flux discontinuity and associated absorption features
matching the Lyman series transitions at z = 0.408 in both sightlines. The HI
column density is log N(HI) = 19.6-19.7 at both locations across the lens,
comparable to what is seen in 21 cm images of nearby ellipticals. The HI gas
kinematics are well-matched with the kinematics of the FeII absorption complex
revealed in ground-based echelle data, displaying a large velocity shear of 360
km/s across the galaxy. We estimate an ISM Fe abundance of 0.3-0.4 solar at
both locations. Including likely dust depletions increases the estimated Fe
abundances to solar or supersolar, similar to those of the hot ISM and stars of
nearby ellipticals. Assuming 100% covering fraction of this Fe-enriched gas,we
infer a total Fe mass of M_cool(Fe)~(5-8)x10^4 M_sun in the cool ISM of the
massive elliptical lens, which is no more than 5% of the total Fe mass observed
in the hot ISM.Comment: 6 pages, 2 figures; Accepted for publication in ApJ Letter
Evidence for Late-Time Feedback from the Discovery of Multiphase Gas in a Massive Elliptical at
We report the first detection of multiphase gas within a quiescent galaxy
beyond . The observations use the brighter image of doubly lensed
QSO HE 00471756 to probe the ISM of the massive () elliptical lens galaxy at .
Using Hubble Space Telescope's Cosmic Origins Spectrograph (COS), we obtain a
medium-resolution FUV spectrum of the lensed QSO and identify numerous
absorption features from in the lens ISM at projected distance
kpc. The column density is with a molecular gas
fraction of , roughly consistent with some local
quiescent galaxies. The new COS spectrum also reveals kinematically complex
absorption features from highly ionized species O VI and N V with column
densities log and log
, among the highest known in
external galaxies. Assuming the high-ionization absorption features originate
in a transient warm (K) phase undergoing radiative cooling from a
hot halo surrounding the galaxy, we infer a mass accretion rate of . The lack of star formation in the lens
suggests the bulk of this flow is returned to the hot halo, implying a heating
rate of . Continuous heating from evolved
stellar populations (primarily SNe Ia but also winds from AGB stars) may
suffice to prevent a large accumulation of cold gas in the ISM, even in the
absence of strong feedback from an active nucleus.Comment: 10 pages, 4 figures. Accepted for publication in ApJ Letters
following a minor revisio
Characterizing Circumgalactic Gas around Massive Ellipticals at z~0.4 - II. Physical Properties and Elemental Abundances
We present a systematic investigation of the circumgalactic medium (CGM)
within projected distances d<160 kpc of luminous red galaxies (LRGs). The
sample comprises 16 intermediate-redshift (z=0.21-0.55) LRGs of stellar mass
M_star>1e11 M_sun. Combining far-ultraviolet Cosmic Origin Spectrograph spectra
from the Hubble Space Telescope and optical echelle spectra from the ground
enables a detailed ionization analysis based on resolved component structures
of a suite of absorption transitions, including the full HI Lyman series and
various ionic metal transitions. By comparing the relative abundances of
different ions in individually-matched components, we show that cool gas (T~1e4
K) density and metallicity can vary by more than a factor of ten in in an LRG
halo. Specifically, metal-poor absorbing components with <1/10 solar
metallicity are seen in 50% of the LRG halos, while gas with solar and
super-solar metallicity is also common. These results indicate a complex
multiphase structure and poor chemical mixing in these quiescent halos. We
calculate the total surface mass density of cool gas, \Sigma_cool, by applying
the estimated ionization fraction corrections to the observed HI column
densities. The radial profile of \Sigma_cool is best-described by a projected
Einasto profile of slope \alpha=1 and scale radius r_s=48 kpc. We find that
typical LRGs at z~0.4 contain cool gas mass of M_cool= (1-2) x1e10 M_sun at
d<160 kpc (or as much as 4x1e10 M_sun at d<500 kpc), comparable to the cool CGM
mass of star-forming galaxies. Furthermore, we show that high-ionization OVI
and low-ionization absorption species exhibit distinct velocity profiles,
highlighting their different physical origins. We discuss the implications of
our findings for the origin and fate of cool gas in LRG halos.Comment: Accepted for publication in MNRAS after a minor revision. 23 pages,
14 figures, and a 29-page Appendix with 27 additional figure
Characterizing Circumgalactic Gas around Massive Ellipticals at z ~ 0.4 I. Initial Results
We present a new Hubble Space Telescope (HST) Cosmic Origins Spectrograph
(COS) absorption-line survey to study halo gas around 16 luminous red galaxies
(LRGs) at z=0.21-0.55. The LRGs are selected uniformly with stellar mass
Mstar>1e11 Msun and no prior knowledge of the presence/absence of any
absorption features. Based on observations of the full Lyman series, we obtain
accurate measurements of neutral hydrogen column density N(HI) and find that
high-N(HI) gas is common in these massive quiescent halos with a median of <log
N(HI)> = 16.6 at projected distances d<~160 kpc. We measure a mean covering
fraction of optically-thick gas with log N(HI)>~17.2 of
LLS=0.44^{+0.12}_{-0.11} at d<~160 kpc and
LLS=0.71^{+0.11}_{-0.20} at d<~100 kpc. The line-of-sight velocity
separations between the HI absorbing gas and LRGs are characterized by a mean
and dispersion of =29 km/s and \sigma_v_{gas-gal}=171 km/s.
Combining COS FUV and ground-based echelle spectra provides an expanded
spectral coverage for multiple ionic transitions, from low-ionization MgII and
SiII, to intermediate ionization SiIII and CIII, and to high-ionization OVI
absorption lines. We find that intermediate ions probed by CIII and SiIII are
the most prominent UV metal lines in LRG halos with a mean covering fraction of
_{0.1}=0.75^{+0.08}_{-0.13} for W(977)>=0.1 Ang at d<160 kpc,
comparable to what is seen for CIII in L* and sub-L* star-forming and red
galaxies but exceeding MgII or OVI in quiescent halos. The COS-LRG survey shows
that massive quiescent halos contain widespread chemically-enriched cool gas
and that little distinction between LRG and star-forming halos is found in
their HI and CIII content.Comment: 19 pages, 6 figures, accepted by MNRA
EMPRESS. VI. Outflows Investigated in Low-Mass Galaxies with : Weak Feedback in Low-Mass Galaxies?
We study emission line profiles of 21 nearby low-mass
() galaxies in deep medium-high resolution spectra taken
with Magellan/MagE. These low-mass galaxies are actively star-forming systems
with high specific star-formation rates of
that are well above the
star-formation main sequence and its extrapolation. We identify broad-line
components of H and [OIII] emission in 14 out of the 21
galaxies that cannot be explained by the MagE instrumental profile or the
natural broadening of line emission. We conduct double Gaussian profile fitting
to the emission of the 14 galaxies, and find that the broad-line components
have line widths significantly larger than those of the narrow-line components,
indicative of galactic outflows. The board-line components have moderately
large line widths of km s. We estimate the maximum outflow
velocities and obtain values of km s,
which are found to be comparable to or slightly larger than the escape
velocities. Positive correlations of with star-formation
rates, stellar masses, and circular velocities, extend down into this low-mass
regime. Broad- to narrow-line flux ratios BNRs are generally found to be
smaller than those of massive galaxies. The small and BNRs
suggest that the mass loading factors can be as small as 0.1 - 1 or
below, in contrast to the large of energy-driven outflows predicted by
numerical simulations.Comment: 22 pages, 11 figures, Accepted for publication by Ap
The Cosmic Ultraviolet Baryon Survey (CUBS) V: On the Thermodynamic Properties of the Cool Circumgalactic Medium at
This paper presents a systematic study of the photoionization and
thermodynamic properties of the cool circumgalactic medium (CGM) as traced by
rest-frame ultraviolet absorption lines around 26 galaxies at redshift
. The study utilizes both high-quality far-ultraviolet and optical
spectra of background QSOs and deep galaxy redshift surveys to characterize the
gas density, temperature, and pressure of individual absorbing components and
to resolve their internal non-thermal motions. The derived gas density spans
more than three decades, from to
, while the temperature of the gas is confined in a narrow range of . In addition, a weak anti-correlation between
gas density and temperature is observed, consistent with the expectation of the
gas being in photoionization equilibrium. Furthermore, decomposing the observed
line widths into thermal and non-thermal contributions reveals that more than
30% of the components at exhibit line widths driven by
non-thermal motions, in comparison to % found at -3.
Attributing the observed non-thermal line widths to intra-clump turbulence, we
find that massive quenched galaxies on average exhibit higher non-thermal
broadening/turbulent energy in their CGM compared to star-forming galaxies at
. Finally, strong absorption features from multiple ions covering
a wide range of ionization energy (e.g., from Mg II to O IV) can be present
simultaneously in a single absorption system with kinematically aligned
component structure, but the inferred pressure in different phases may differ
by a factor of .Comment: 16 pages, 4 figures, 1 table, accepted for publication in MNRA