Gas in galactic halos

2012 ◽  
Vol 10 (H16) ◽  
pp. 596-597
Author(s):  
Ralf-Jürgen Dettmar
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Observational Evidence ◽  
Molecular Gas ◽  
Galactic Halos ◽  
Feedback Mechanisms ◽  
X Ray

AbstractThe interstellar medium in galactic halos is described as a consequence of feedback mechanisms from processes related to star-formation in the disk. The presence of gas in galactic halos is also expected due to accretion of gas from the circumgalactic environment. The observational evidence for gas in galactic halos - from the hot X-ray emitting coronal phase to cool molecular gas and dust - is reviewed and discussed in the context of current models of the ISM and the “infall vs. outflow“ debate.

scholarly journals Hard X-Ray Irradiation Potentially Drives Negative AGN Feedback by Altering Molecular Gas Properties

2021 ◽  
Vol 257 (2) ◽  
pp. 64
Author(s):  
Taiki Kawamuro ◽  
Claudio Ricci ◽  
Takuma Izumi ◽  
Masatoshi Imanishi ◽  
Shunsuke Baba ◽  
...  
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Active Galactic Nucleus ◽  
Accretion Rate ◽  
Spatial Separation ◽  
Molecular Gas ◽  
X Ray ◽  
Mass Accretion Rate ◽  
Nuclear Regions

Abstract To investigate the role of active galactic nucleus (AGN) X-ray irradiation on the interstellar medium (ISM), we systematically analyzed Chandra and Atacama Large Millimeter/submillimeter Array CO (J = 2–1) data for 26 hard X-ray (>10 keV) selected AGNs at redshifts below 0.05. While Chandra unveils the distribution of X-ray-irradiated gas via Fe-Kα emission, the CO (J = 2–1) observations reveal that of cold molecular gas. At high resolutions ≲1″, we derive Fe-Kα and CO (J = 2–1) maps for the nuclear 2″ region and for the external annular region of 2″–4″, where 2″ is ∼100–600 pc for most of our AGNs. First, focusing on the external regions, we find the Fe-Kα emission for six AGNs above 2σ. Their large equivalent widths (≳1 keV) suggest a fluorescent process as their origin. Moreover, by comparing the 6–7 keV/3–6 keV ratio, as a proxy of Fe-Kα, and CO (J = 2–1) images for three AGNs with the highest significant Fe-Kα detections, we find a possible spatial separation. These suggest the presence of X-ray-irradiated ISM and the change in the ISM properties. Next, examining the nuclear regions, we find that (1) the 20–50 keV luminosity increases with the CO (J = 2–1) luminosity; (2) the ratio of CO (J = 2–1)/HCN (J = 1–0) luminosities increases with 20–50 keV luminosity, suggesting a decrease in the dense gas fraction with X-ray luminosity; and (3) the Fe-Kα-to-X-ray continuum luminosity ratio decreases with the molecular gas mass. This may be explained by a negative AGN feedback scenario: the mass accretion rate increases with gas mass, and simultaneously, the AGN evaporates a portion of the gas, which possibly affects star formation.

Molecular Clouds

1977 ◽  
Vol 75 ◽  
pp. 37-54 ◽  
Author(s):  
P. Thaddeus
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Molecular Clouds ◽  
Physical State ◽  
Molecular Gas ◽  
Spectroscopic Techniques ◽  
Low Density ◽  
Recombination Line ◽  
Interstellar Gas ◽  
Impossible Task

To attempt to understand star formation without knowing the physical state of the dense interstellar molecular gas from which stars are made is an almost impossible task. Star formation has developed late as a branch of astrophysics largely for lack of observational data, and in particular, has lagged badly behind the study of the atomic and ionized components of the interstellar gas because spectroscopic techniques which work well at low density have an unfortunate tendency to fail when the density is high. Optical spectroscopy, which has been applied to the interstellar medium for over 70 years, has made little progress in regions of high density because of obscuration, and the same is true a fortiori of spacecraft spectroscopy in the UV; radio 21-cm and recombination line observations, although unhampered by obscuration, are unsatisfactory because the dense condensations are almost entirely molecular in composition.

scholarly journals Molecular gas in galaxies: changing conditions from disks to starbursts

2015 ◽  
Vol 11 (S315) ◽  
pp. 199-206
Author(s):  
Christine D. Wilson
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Galaxy Evolution ◽  
Surface Density ◽  
Physical State ◽  
Active Galaxies ◽  
Molecular Gas ◽  
Central Question ◽  
Space Observatory ◽  
Nearby Galaxies

AbstractIn understanding galaxy evolution, one central question is how star formation is regulated in galaxies. Changes in star formation rates are likely tied to changes in the interstellar medium, particularly the molecular gas which is the fuel for star formation. I will discuss our recent results which use data from the Herschel Space Observatory, the Atacama Large Millimeter/submillimeter Array, and other telescopes to determine the typical density, temperature, and surface density of the molecular gas in various nearby galaxies. Comparing the properties of molecular gas in starburst and other active galaxies with more quiescent spiral disks provides some clues as to how changes in the physical state of the gas, such as mean density, can lead to enhanced star formation rates.

scholarly journals Star Formation and Molecular Gas in Extremely Metal-poor Galaxies: Insights from the Thermal Balance in the Neutral Gas

2018 ◽  
Vol 14 (S344) ◽  
pp. 259-262 ◽  
Author(s):  
Vianney Lebouteiller
Keyword(s):  
Star Formation ◽  
Dwarf Galaxy ◽  
Large Fraction ◽  
Formation Rate ◽  
Conversion Function ◽  
Molecular Gas ◽  
Apparent Lack ◽  
X Ray ◽  
Heating Mechanism ◽  
Neutral Gas

AbstractThe apparent lack of cold molecular gas in blue compact dwarf (BCD) galaxies is at variance with their intense star-formation episode. The CO molecule, often used a tracer of H2 through a conversion function, is selectively photodissociated in dust-poor environments and, as a result, a potentially large fraction of H2 is expected to reside in the so-called CO-dark gas, where it could be traced instead by infrared cooling lines [CI], [CII], and [OI]. Although the fraction of CO-dark gas to total molecular gas is in theory expected to be relatively large in metal-poor galaxies, many uncertainties remain due to the difficulty in identifying the main heating mechanism associated to the cooling lines observed in such galaxies.Investigations of the Herschel Dwarf Galaxy Survey (DGS; Madden et al.2013) show that the heating mechanism in the neutral gas of BCDs cannot be dominated by the photoelectric effect on dust grains below some threshold metallicity due to the low abundance of dust and polycyclic aromatic hydrocarbons, implying that other heating mechanisms need to be invoked, along with a new interpretation of the corresponding infrared line diagnostics. In the study presented here and in Lebouteiller et al. (2017), we use optical and infrared lines to constrain the physical conditions in the HII region + HI region of the BCD I Zw 18 (18 Mpc; ≍2% solar metallicity) within a consistent photoionization and photodissociation model. We show that the HI region is entirely heated by a single ultraluminous X-ray source with important consequences on the applicability of [CII] to trace the star-formation rate and to trace the CO-dark gas. We derive stringent upper limits on the size of H2 clumps that may be detected in the future with JWST and IRAM/NOEMA. We also show that the nature of the X-ray source can be inferred from the corresponding signatures in the ISM. Finally we speculate that star formation may be quenched in extremely metal-poor dwarf galaxies due to X-ray photoionization.

scholarly journals Arp 220 – IC 4553/4: understanding the system and diagnosing the ISM

2007 ◽  
Vol 3 (S242) ◽  
pp. 437-445
Author(s):  
W. A. Baan
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Observational Data ◽  
X Ray ◽  
Infrared Galaxy ◽  
Luminous Infrared Galaxy

AbstractArp 220 is a nearby system in final stages of galaxy merger with powerful ongoing star-formation at and surrounding the two nuclei. Arp 220 was detected in HI absorption and OH Megamaser emission and later recognized as the nearest ultra-luminous infrared galaxy also showing powerful molecular and X-ray emissions. In this paper we review the available radio and mm-wave observational data of Arp 220 in order to obtain an integrated picture of the dense interstellar medium that forms the location of the powerful star-formation at the two nuclei.

scholarly journals Molecular gas in the central region of NGC 7213

2020 ◽  
Vol 641 ◽  
pp. A151
Author(s):  
F. Salvestrini ◽  
C. Gruppioni ◽  
F. Pozzi ◽  
C. Vignali ◽  
A. Giannetti ◽  
...  
Keyword(s):  
Star Formation ◽  
Emission Line ◽  
Large Scale ◽  
Host Galaxy ◽  
Molecular Gas ◽  
X Ray ◽  
Gas Kinematics ◽  
Star Formation Activity ◽  
Multi Wavelength

We present a multi-wavelength study (from X-ray to mm) of the nearby low-luminosity active galactic nucleus NGC 7213. We combine the information from the different bands to characterise the source in terms of contribution from the AGN and the host-galaxy interstellar medium. This approach allows us to provide a coherent picture of the role of the AGN and its impact, if any, on the star formation and molecular gas properties of the host galaxy. We focused our study on archival ALMA Cycle 1 observations, where the CO(2–1) emission line has been used as a tracer of the molecular gas. Using the 3DBAROLO code on ALMA data, we performed the modelling of the molecular gas kinematics traced by the CO(2–1) emission, finding a rotationally dominated pattern. The molecular gas mass of the host galaxy was estimated from the integrated CO(2–1) emission line obtained with APEX data, assuming an αCO conversion factor. Had we used the ALMA data, we would have underestimated the gas masses by a factor ∼3, given the filtering out of the large-scale emission in interferometric observations. We also performed a complete X-ray spectral analysis on archival observations, revealing a relatively faint and unobscured AGN. The AGN proved to be too faint to significantly affect the properties of the host galaxy, such as star formation activity and molecular gas kinematics and distribution.

scholarly journals Abundant molecular gas and inefficient SF in intra-cluster regions of a ram pressure stripped tail

2014 ◽  
Vol 10 (S309) ◽  
pp. 227-229
Author(s):  
P. Jáchym ◽  
M. Sun ◽  
F. Combes ◽  
L. Cortese ◽  
J. D. P. Kenney
Keyword(s):  
Star Formation ◽  
Molecular Gas ◽  
X Ray ◽  
Star Forming ◽  
Ram Pressure ◽  
Formation Efficiency ◽  
First Time

AbstractFor the first time in any ram pressure stripped galaxy, we detect large amounts of cold molecular gas in the X-ray bright, and star forming tail of ESO 137-001 in the Norma cluster. We find very low star formation efficiency in the stripped gas, similar to values found in the outer spiral disks where however molecular gas is mostly undetected. The results were recently published in Jáchym et al. (2014).

Molecular gas, the interstellar medium, and star formation in S0 and SA galaxies

1989 ◽  
Vol 344 ◽  
pp. 747 ◽  
Author(s):  
Harley A., Jr. Thronson ◽  
Linda Tacconi ◽  
Jeffrey Kenney ◽  
Matthew A. Greenhouse ◽  
Michael Margulis ◽  
...  
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Molecular Gas

scholarly journals Sequentially triggered star formation in OB associations

2006 ◽  
Vol 2 (S237) ◽  
pp. 270-277 ◽  
Author(s):  
Thomas Preibisch ◽  
Hans Zinnecker
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Formation Process ◽  
Large Scale ◽  
Observational Evidence ◽  
Star Formation History ◽  
The Sun ◽  
Formation History ◽  
Triggering Mechanisms ◽  
Ob Associations

AbstractWe discuss observational evidence for sequential and triggered star formation in OB associations. We first review the star formation process in the Scorpius-Centaurus OB association, the nearest OB association to the Sun, where several recent extensive studies have allowed us to reconstruct the star formation history in a rather detailed way. We then compare the observational results with those obtained for other OB associations and with recent models of rapid cloud and star formation in the turbulent interstellar medium. We conclude that the formation of whole OB subgroups (each consisting of several thousand stars) requires large-scale triggering mechanisms such as shocks from expanding wind and supernova driven superbubbles surrounding older subgroups. Other triggering mechanisms, like radiatively driven implosion of globules, also operate, but seem to be secondary processes, forming only small stellar groups rather than whole OB subgroups with thousands of stars.

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