54 research outputs found
The Impact of Starbursts on the Circumgalactic Medium
We present a study exploring the impact of a starburst on the properties of
the surrounding circum-galactic medium (CGM): gas located beyond the galaxy's
stellar body and extending out to the virial radius (200 kpc). We obtained
ultraviolet spectroscopic data from the Cosmic Origin Spectrograph (COS)
probing the CGM of 20 low-redshift foreground galaxies using background QSOs.
Our sample consists of starburst and control galaxies. The latter comprises
normal star-forming and passive galaxies with similar stellar masses and impact
parameters as the starbursts. We used optical spectra from the Sloan Digital
Sky Survey(SDSS) to estimate the properties of the starbursts, inferring
average ages of 200 Myrs and burst fractions involving ~10% of their stellar
mass. The COS data reveal highly ionized gas traced by CIV in 80%(4/5) of the
starburst and in 17%(2/12) of the control sample. The two control galaxies with
CIV absorbers differed from the four starbursts in showing multiple
low-ionization transitions and strong saturated Lyman-alpha lines. They
therefore appear to be physically different systems. We show that the CIV
absorbers in the starburst CGM represent a significant baryon repository. The
high detection rate of this highly ionized material in the starbursts suggests
that starburst-driven winds can affect the CGM out to radii as large as 200
kpc. This is plausible given the inferred properties of the starbursts and the
known properties of starburst-driven winds. This would represent the first
direct observational evidence of local starbursts impacting the bulk of their
gaseous halos, and as such provides new evidence of the importance of this kind
of feedback in the evolution of galaxies.Comment: Accepted for publication in Ap
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
The morphology and kinematics of the gaseous circumgalactic medium of Milky Way mass galaxies -- II. comparison of IllustrisTNG and Illustris simulation results
We have carried out a controlled comparison of the structural and kinematic
properties of the circumgalactic medium (CGM) around Milky Way mass galaxies in
the Illustris and IllustrisTNG simulations. Very striking differences are
found. At z=0, gas column density and temperature profiles at large radii
( kpc) correlate strongly with disk gas mass fraction in Illustris,
but not in TNG. The neutral gas at large radii is preferentially aligned in the
plane of the disk in TNG, whereas it is much more isotropic in Illustris. The
vertical coherence scale of the rotationally supported gas in the CGM is linked
to the gas mass fraction of the galaxy in Illustris, but not in TNG. A tracer
particle analysis allows us to show how these differences can be understood as
a consequence of the different sub-grid models of feedback in the two
simulations. A study of spatially matched galaxies in the two simulations shows
that in TNG, feedback by supernovae and AGN helps to create an extended smooth
reservoir of hot gas at high redshifts, that then cools to form a thin,
rotationally-supported disk at later times. In Illustris, AGN dump heat in the
form of hot gas bubbles that push diffuse material at large radii out of the
halo. The disk is formed by accretion of colder, recycled material, and this
results in more vertically extended gas distributions above and below the
Galactic plane. We conclude that variations in the structure of gas around
Milky Way mass galaxies are a sensitive probe of feedback physics in
simulations and are worthy of more observational consideration in future.Comment: 16 pages, 14 figures, accepted for publication in MNRA
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