85 research outputs found
COS-Burst : observations of the impact of starburst-driven winds on the properties of the circum-galactic medium
V.W. acknowledges the support of the European Research Council via the award of a starting grant (SEDMorph: P.I. V. Wild).We report on observations made with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) using background QSOs to probe the circum-galactic medium (CGM) around 17 low-redshift galaxies thatare undergoing or have recently undergone a strong starburst (the COS-Burst program). The sight lines extend out to roughly the virial radius of the galaxy halo. We construct control samples of normal star-forming low-redshift galaxies from the COS/HST archive that match the starbursts in terms of galaxy stellar mass and impact parameter. We find clear evidence that the CGM around the starbursts differs systematically compared to the control galaxies. The Lyα, Si III,C IV, and possibly O VI absorption-lines are stronger as a function of impact parameter, and the ratios of the equivalent widths of CIV/Lyα and Si III/Lyα are both larger than in normal star-forming galaxies. We also find that the widths and the velocity offsets (relative to vsys) of the Lyα absorption-lines are significantly larger in the CGM of the starbursts, implying velocities of the absorbing material that are roughly twice the halo virial velocity. We show that these properties can be understood as a consequence of the interaction between a starburst-driven wind and the pre-existing CGM. These results underscore the importance of winds driven from intensely star-forming galaxies in helping drive the evolution of galaxies and the intergalactic medium. They also offer anew probe of the properties of starburst-driven winds and of the CGM itself.Publisher PDFPeer reviewe
Spatially Resolved Galactic Wind in Lensed Galaxy RCSGA 032727-132609
We probe the spatial distribution of outflowing gas along four lines of sight
separated by up to 6 kpc in a gravitationally-lensed star-forming galaxy at
z=1.70. Using MgII and FeII emission and absorption as tracers, we find that
the clumps of star formation are driving galactic outflows with velocities of
-170 to -250 km/sec. The velocities of MgII emission are redshifted with
respect to the systemic velocities of the galaxy, consistent with being
back-scattered. By contrast, the FeII fluorescent emission lines are either
slightly blueshifted or at the systemic velocity of the galaxy. Taken together,
the velocity structure of the MgII and FeII emission is consistent with arising
through scattering in galactic winds. Assuming a thin shell geometry for the
out owing gas, the estimated masses carried out by these outfows are large (>
30 - 50 ), with mass loading factors several times the
star-formation rate. Almost 20% to 50% of the blueshifted absorption probably
escapes the gravitational potential of the galaxy. In this galaxy, the outflow
is "locally sourced", that is, the properties of the outflow in each line of
sight are dominated by the properties of the nearest clump of star formation;
the wind is not global to the galaxy. The mass outflow rates and the momentum
flux carried out by outflows in individual star forming knots of this object
are comparable to that of starburst galaxies in the local Universe.Comment: 19 pages, 10 figure, accepted for publication in MNRA
The Sunburst Arc: Direct Lyman {\alpha} escape observed in the brightest known lensed galaxy
We present rest-frame ultraviolet and optical spectroscopy of the brightest
lensed galaxy yet discovered, at redshift z = 2.4. This source reveals a
characteristic, triple-peaked Lyman {\alpha} profile which has been predicted
by various theoretical works but to our knowledge has not been unambiguously
observed previously. The feature is well fit by a superposition of two
components: a double-peak profile emerging from substantial radiative transfer,
and a narrow, central component resulting from directly escaping Lyman {\alpha}
photons; but is poorly fit by either component alone. We demonstrate that the
feature is unlikely to contain contamination from nearby sources, and that the
central peak is unaffected by radiative transfer effects apart from very slight
absorption. The feature is detected at signal-to-noise ratios exceeding 80 per
pixel at line center, and bears strong resemblance to synthetic profiles
predicted by numerical models.Comment: Accepted for publication in Astronomy & Astrophysics. 4 pages, 5
figure
EIGER II. first spectroscopic characterisation of the young stars and ionised gas associated with strong H and [OIII] line-emission in galaxies at z=5-7 with JWST
We present emission-line measurements and physical interpretations for a
sample of 117 [OIII] emitting galaxies at , using the first deep
JWST/NIRCam wide field slitless spectroscopic observations. Our 9.7-hour
integration is centered upon the quasar J0100+2802 -- the first of six
fields targeted by the EIGER survey -- and covers microns. We
detect 133 [OIII] doublets, but merge pairs within 10 kpc and 600 km
s, motivated by their small scale clustering excess. We detect H
in 68 and H emission in two galaxies. The galaxies are characterised by
a UV luminosity M ( to ), stellar mass
~ M, H and [OIII] EWs 850
Angstrom (up to 3000 Angstrom), young ages (~100 Myr), a highly excited
interstellar medium ([OIII]/H) and low dust attenuations. These
high EWs are very rare in the local Universe, but we show they are ubiquitous
at based on the measured number densities. The stacked spectrum
reveals H and [OIII] which shows that the galaxies are
typically dust and metal poor (E(B-V)=0.1, 12+log(O/H)=7.4) with a high
electron temperature ( K) and a production efficiency of ionising
photons ( Hz erg). We further show the
existence of a strong mass-metallicity relation. The young highly ionising
stellar populations, moderately low metallicities, low dust attenuations and
high ionisation state in z~6 galaxies conspire to maximise the [OIII] output
from galaxies, yielding an [OIII] luminosity density at z~6 that is
significantly higher than at z~2, despite the order of magnitude decline in
cosmic star formation. Thus, [OIII] emission-line surveys with JWST prove a
highly efficient method to trace the galaxy density in the epoch of
reionization.Comment: Accepted for publication in ApJ. Main text 22 pages, 20 figures. Main
results in Figs 14 (Xi_ion), 15 (MEx diagram),17 (MZR), 19 ([OIII] luminosity
density
A Deep Search For Faint Galaxies Associated With Very Low-redshift C IV Absorbers: III. The Mass- and Environment-dependent Circumgalactic Medium
Using Hubble Space Telescope Cosmic Origins Spectrograph observations of 89
QSO sightlines through the Sloan Digital Sky Survey footprint, we study the
relationships between C IV absorption systems and the properties of nearby
galaxies as well as large-scale environment. To maintain sensitivity to very
faint galaxies, we restrict our sample to 0.0015 < z < 0.015, which defines a
complete galaxy survey to L > 0.01 L* or stellar mass log M_* > 8 Msun. We
report two principal findings. First, for galaxies with impact parameter rho <
1 rvir, C IV detection strongly depends on the luminosity/stellar mass of the
nearby galaxy. C IV is preferentially associated with galaxies with log M_* >
9.5 Msun; lower mass galaxies rarely exhibit significant C IV absorption
(covering fraction f = 9 +12-6% for 11 galaxies with log M_* < 9.5 Msun).
Second, C IV detection within the log M_* > 9.5 Msun population depends on
environment. Using a fixed-aperture environmental density metric for galaxies
with rho < 160 kpc at z < 0.055, we find that 57+/-12% (8/14) of galaxies in
low-density regions (regions with fewer than seven L > 0.15 L* galaxies within
1.5 Mpc) have affiliated C IV absorption; however, none (0/7) of the galaxies
in denser regions show C IV. Similarly, the C IV detection rate is lower for
galaxies residing in groups with dark-matter halo masses of log Mhalo > 12.5
Msun. In contrast to C IV, H I is pervasive in the CGM without regard to mass
or environment. These results indicate that C IV absorbers with log N(C IV) >
13.5 cm^-2 trace the halos of log M_* > 9.5 Msun galaxies but also reflect
larger scale environmental conditions.Comment: 26 pages, 13 figures. ApJ, in pres
Connection Between the Circumgalactic Medium and the Interstellar Medium of Galaxies: Results from the COS-GASS Survey
We present a study exploring the nature and properties of the Circum-Galactic
Medium (CGM) and its connection to the atomic gas content in the interstellar
medium (ISM) of galaxies as traced by the HI 21cm line. Our sample includes 45
low-z (0.026-0.049) galaxies from the GALEX Arecibo SDSS Survey. Their CGM was
probed via absorption in the spectra of background Quasi-Stellar Objects at
impact parameters of 63 to 231kpc. The spectra were obtained with the Cosmic
Origins Spectrograph aboard the Hubble Space Telescope. We detected neutral
hydrogen (Ly absorption-lines) in the CGM of 92% of the galaxies. We
find the radial profile of the CGM as traced by the Ly equivalent width
can be fit as an exponential with a scale length of roughly the virial radius
of the dark matter halo. We found no correlation between the orientation of
sightline relative to the galaxy major axis and the Ly equivalent
width. The velocity spread of the circumgalactic gas is consistent with that
seen in the atomic gas in the interstellar medium. We find a strong correlation
(99.8% confidence) between the gas fraction (M(HI)/M*) and the
impact-parameter-corrected Ly equivalent width. This is stronger than
the analogous correlation between corrected Ly equivalent width and
SFR/M* (97.5% confidence). These results imply a physical connection between
the HI disk and the CGM, which is on scales an order-of-magnitude larger. This
is consistent with the picture in which the HI disk is nourished by accretion
of gas from the CGM.Comment: 13 pages, 9 figures, and 2 tables. Submitted to Ap
Compact [C II] emitters around a C IV absorption complex at redshift 5.7
The physical conditions of the circumgalactic medium are probed by
intervening absorption-line systems in the spectrum of background quasi-stellar
objects out to the epoch of cosmic reionization. A correlation between the
ionization state of the absorbing gas and the nature of the nearby galaxies has
been suggested by the sources detected either in Lyalpha or [C ii] 158 m near
to respectively highly-ionized and neutral absorbers. This is also likely
linked to the global changes in the incidence of absorption systems of
different types and the process of cosmic reionization. Here we report the
detection of two [C ii]-emitting galaxies at redshift that are
associated with a complex high-ionization C iv absorption system. These objects
are part of an overdensity of galaxies and have compact sizes (< 2.4 kpc) and
narrow line widths (FWHM 62--64 km s-1). Hydrodynamic simulations
predict that similar narrow [C ii] emission may arise from the heating of small
( 3 kpc) clumps of cold neutral medium or a compact photodissociation
region. The lack of counterparts in the rest-frame ultraviolet indicates severe
obscuration of the sources that are exciting the [C ii] emission. These results
may suggest a connection between the properties of the [C ii] emission, the
rare overdensity of galaxies and the unusual high ionization state of the gas
in this region.Comment: Published in Nature on 10 May 2023; authors' version; link to the
paper: https://www.nature.com/articles/s41586-023-05901-
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