scholarly journals Physical conditions in the gas phases of the giant H II region LMC-N 11

2019 ◽  
Vol 632 ◽  
pp. A106 ◽  
Author(s):  
V. Lebouteiller ◽  
D. Cormier ◽  
S. C. Madden ◽  
M. Galametz ◽  
S. Hony ◽  
...  
Keyword(s):  
Column Density ◽  
Formation Rate ◽  
Large Magellanic Cloud ◽  
Photoelectric Effect ◽  
Gas Content ◽  
Molecular Gas ◽  
Heating Efficiency ◽  
Physical Conditions ◽  
Atomic Gas ◽  
Statistical Trends

Context. The ambiguous origin of the [C II] 158μm line in the interstellar medium complicates its use for diagnostics concerning the star-formation rate and physical conditions in photodissociation regions. Aims. We investigate the origin of [C II] in order to measure the total molecular gas content, the fraction of CO-dark H2 gas, and how these parameters are impacted by environmental effects such as stellar feedback. Methods. We observed the giant H II region N 11 in the Large Magellanic Cloud with SOFIA/GREAT. The [C II] line is resolved in velocity and compared to H I and CO, using a Bayesian approach to decompose the line profiles. A simple model accounting for collisions in the neutral atomic and molecular gas was used in order to derive the H2 column density traced by C+. Results. The profile of [C II] most closely resembles that of CO, but the integrated [C II] line width lies between that of CO and that of H I. Using various methods, we find that [C II] mostly originates from the neutral gas. We show that [C II] mostly traces the CO-dark H2 gas but there is evidence of a weak contribution from neutral atomic gas preferentially in the faintest components (as opposed to components with low [C II]/CO or low CO column density). Most of the molecular gas is CO-dark. The CO-dark H2 gas, whose density is typically a few 100s cm−3 and thermal pressure in the range 103.5−5 K cm−3, is not always in pressure equilibrium with the neutral atomic gas. The fraction of CO-dark H2 gas decreases with increasing CO column density, with a slope that seems to depend on the impinging radiation field from nearby massive stars. Finally we extend previous measurements of the photoelectric-effect heating efficiency, which we find is constant across regions probed with Herschel, with [C II] and [O I] being the main coolants in faint and diffuse, and bright and compact regions, respectively, and with polycyclic aromatic hydrocarbon emission tracing the CO-dark H2 gas heating where [C II] and [O I] emit. Conclusions. We present an innovative spectral decomposition method that allows statistical trends to be derived for the molecular gas content using CO, [C II], and H I profiles. Our study highlights the importance of velocity-resolved photodissociation region (PDR) diagnostics and higher spatial resolution for H I observations as future steps.

scholarly journals Molecular Gas in the Magellanic Clouds

1999 ◽  
Vol 190 ◽  
pp. 67-73 ◽  
Author(s):  
Mónica Rubio
Keyword(s):  
Line Emission ◽  
Magellanic Clouds ◽  
Gas Content ◽  
Molecular Gas ◽  
Star Forming ◽  
Physical Conditions ◽  
Star Forming Regions ◽  
Hydrogen Column Density ◽  
Spatial Coverage ◽  
Co Emission

The molecular gas content in the Magellanic Clouds has been studied, with different spatial coverage and resolution, through obervations of CO(1-0) line emission. In the LMC and the SMC the molecular gas is dominated by clouds whose properties are different from those of their Galactic counterparts. The relation between the intensity of CO emission and molecular hydrogen column density, or the conversion factor X, is different than that of molecular clouds in our Galaxy and depends on the ambient physical conditions. Studying the molecular gas through observations in the H2 emission line may prove an alternative way to determine the molecular content associated with star forming regions in the Magellanic Clouds. In particular, results obtained towards 30 Doradus in the LMC are presented.

scholarly journals New constraints on the physical conditions in H2-bearing GRB-host damped Lyman-α absorbers

2019 ◽  
Vol 629 ◽  
pp. A131 ◽  
Author(s):  
K. E. Heintz ◽  
J. Bolmer ◽  
C. Ledoux ◽  
P. Noterdaeme ◽  
J.-K. Krogager ◽  
...  
Keyword(s):  
Molecular Hydrogen ◽  
Gas Content ◽  
Host Galaxy ◽  
Molecular Gas ◽  
Line Profiles ◽  
Vibrationally Excited ◽  
Physical Conditions ◽  
Very Large Telescope ◽  
Molecular Fraction ◽  
Low Metallicity

We report the detections of molecular hydrogen (H2), vibrationally-excited H2 (H2∗), and neutral atomic carbon (C I), an efficient tracer of molecular gas, in two new afterglow spectra of GRBs 181020A (z = 2.938) and 190114A (z = 3.376), observed with X-shooter at the Very Large Telescope (VLT). Both host-galaxy absorption systems are characterized by strong damped Lyman-α absorbers (DLAs) and substantial amounts of molecular hydrogen with logN(H I, H2) = 22.20 ± 0.05,  20.40 ± 0.04 (GRB 181020A) and logN(H I, H2) = 22.15 ± 0.05,  19.44 ± 0.04 (GRB 190114A). The DLA metallicites, depletion levels, and dust extinctions are within the typical regimes probed by GRBs with [Zn/H] = −1.57 ± 0.06, [Zn/Fe] = 0.67 ± 0.03, and AV = 0.27 ± 0.02 mag (GRB 181020A) and [Zn/H] = −1.23 ± 0.07, [Zn/Fe] = 1.06 ± 0.08, and AV = 0.36 ± 0.02 mag (GRB 190114A). In addition, we examine the molecular gas content of all known H2-bearing GRB-DLAs and explore the physical conditions and characteristics required to simultaneously probe C I and H2∗. We confirm that H2 is detected in all C I- and H2∗-bearing GRB absorption systems, but that these rarer features are not necessarily detected in all GRB H2 absorbers. We find that a large molecular fraction of fH2 ≳ 10−3 is required for C I to be detected. The defining characteristic for H2∗ to be present is less clear, though a large H2 column density is an essential factor. We also find that the observed line profiles of the molecular-gas tracers are kinematically “cold”, with small velocity offsets of δv <  20 km s−1 from the bulk of the neutral absorbing gas. We then derive the H2 excitation temperatures of the molecular gas and find that they are relatively low with Tex ≈ 100−300 K, however, there could be evidence of warmer components populating the high-J H2 levels in GRBs 181020A and 190114A. Finally, we demonstrate that even though the X-shooter GRB afterglow campaign has been successful in recovering several H2-bearing GRB-host absorbers, this sample is still hampered by a significant dust bias excluding the most dust-obscured H2 absorbers from identification. C I and H2∗ could open a potential route to identify molecular gas even in low-metallicity or highly dust-obscured bursts, though they are only efficient tracers for the most H2-rich GRB-host absorption systems.

scholarly journals Molecular gas in the Small Magellanic Cloud

1991 ◽  
Vol 148 ◽  
pp. 429-430
Author(s):  
Monica Rubio
Keyword(s):  
Molecular Hydrogen ◽  
Molecular Clouds ◽  
Column Density ◽  
Angular Resolution ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Molecular Gas ◽  
Small Magellanic Cloud ◽  
Hydrogen Column Density ◽  
Co Emission

We summarize the results of observations of molecular gas from the Small Magellanic Cloud (SMC) made with low angular resolution (8'.8). These observations show that the CO emission is weak (TA˜ 0.04K) and that the CO luminosities of the Clouds are low compared to those of Galactic molecular clouds. The factor to convert the CO luminosity to molecular hydrogen column density for the SMC is ˜20 and three times larger than those derived for clouds in our Galaxy and in the Large Magellanic Cloud (LMC) respectively. In addition, we present preliminary results of high resolution (40″) observations of SMC molecular clouds made with the SEST telescope.

scholarly journals Molecular Gas and Star Formation in Local Early–type Galaxies

2010 ◽  
Vol 6 (S277) ◽  
pp. 55-58
Author(s):  
M. Bureau ◽  
T. A. Davis ◽  
K. Alatalo ◽  
A. F. Crocker ◽  
L. Blitz ◽  
...  
Keyword(s):  
Star Formation ◽  
Far Infrared ◽  
Gas Content ◽  
Molecular Gas ◽  
Disk Galaxies ◽  
Formation Processes ◽  
Early Type ◽  
High Detection Rate ◽  
Physical Conditions ◽  
Multi Wavelength

AbstractThe molecular gas content of local early-type galaxies is constrained and discussed in relation to their evolution. First, as part of the ATLAS3D survey, we present the first complete, large (260 objects), volume-limited single-dish survey of CO in normal local early-type galaxies. We find a surprisingly high detection rate of 22%, independent of luminosity and at best weakly dependent on environment. Second, the extent of the molecular gas is constrained with CO synthesis imaging, and a variety of morphologies is revealed. The kinematics of the molecular gas and stars are often misaligned, implying an external gas origin in over a third of the systems, although this behaviour is drastically diffferent between field and cluster environments. Third, many objects appear to be in the process of forming regular kpc-size decoupled disks, and a star formation sequence can be sketched by piecing together multi-wavelength information on the molecular gas, current star formation, and young stars. Last, early-type galaxies do not seem to systematically obey all our usual prejudices regarding star formation, following the standard Schmidt-Kennicutt law but not the far infrared-radio correlation. This may suggest a greater diversity in star formation processes than observed in disk galaxies. Using multiple molecular tracers, we are thus starting to probe the physical conditions of the cold gas in early-types.

scholarly journals PHIBSS2: survey design and z = 0.5 – 0.8 results

2019 ◽  
Vol 622 ◽  
pp. A105 ◽  
Author(s):  
J. Freundlich ◽  
F. Combes ◽  
L. J. Tacconi ◽  
R. Genzel ◽  
S. Garcia-Burillo ◽  
...  
Keyword(s):  
Star Formation ◽  
Survey Design ◽  
Formation Rate ◽  
Sample Selection ◽  
Stellar Mass ◽  
Gas Content ◽  
Molecular Gas ◽  
Star Forming ◽  
Gas Measurements ◽  
Deep Fields

Following the success of the Plateau de Bure high-z Blue Sequence Survey (PHIBSS), we present the PHIBSS2 legacy program, a survey of the molecular gas properties of star-forming galaxies on and around the star-formation main sequence (MS) at different redshifts using IRAM’s NOrthern Extended Millimeter Array (NOEMA). This survey significantly extends the existing sample of star-forming galaxies with CO molecular gas measurements, probing the peak epoch of star formation (z = 1 − 1.6) as well as its building-up (z = 2 − 3) and winding-down (z = 0.5 − 0.8) phases. The targets are drawn from the well-studied GOODS, COSMOS, and AEGIS cosmological deep fields and uniformly sample the MS in the stellar mass (M⋆) – star formation rate (SFR) plane with log(M⋆/M⊙) = 10 − 11.8 and SFR = 3.5 − 500 M⊙ yr−1 without morphological selection, thus providing a statistically meaningful census of star-forming galaxies at different epochs. We describe the survey strategy and sample selection before focusing on the results obtained at redshift z = 0.5 − 0.8, where we report 60 CO(2-1) detections out of 61 targets. We determine molecular gas masses between 2 × 109 and 5 × 1010 M⊙ and separately obtain disc sizes and bulge-to-total (B/T) luminosity ratios from HST I-band images. The median molecular gas-to-stellar mass ratio μgas∼ = 0.28 ± 0.04, gas fraction fgas∼ = 0.22 ± 0.02, and depletion time $ \widetilde{t_{\mathrm{depl}}} = 0.84 \pm 0.07\,\mathrm{Gyr} $ as well as their dependence with stellar mass and offset from the MS follow published scaling relations for a much larger sample of galaxies spanning a significantly wider range of redshifts, the cosmic evolution of the SFR being mainly driven by that of the molecular gas fraction. The galaxy-averaged molecular Kennicutt–Schmidt (KS) relation between molecular gas and SFR surface densities is strikingly linear, pointing towards similar star formation timescales within galaxies at any given epoch. In terms of morphology, the molecular gas content, the SFR, the disc stellar mass, and the disc molecular gas fraction do not seem to correlate with B/T and the stellar surface density, which suggests an ongoing supply of fresh molecular gas to compensate for the build-up of the bulge. Our measurements do not yield any significant variation of the depletion time with B/T and hence no strong evidence for morphological quenching within the scatter of the MS.

scholarly journals CO Emission toward HI Absorption Sources in the Large Magellanic Cloud

1999 ◽  
Vol 190 ◽  
pp. 124-125
Author(s):  
M. Marx-Zimmer ◽  
F. Zimmer ◽  
U. Herbstmeier ◽  
J. M. Dickey
Keyword(s):  
Milky Way ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Molecular Gas ◽  
Atomic Gas ◽  
Co Emission

In the Large Magellanic Cloud (LMC) a large number of cool HI clouds have been detected with temperatures much lower than those found for atomic clouds in the Milky Way (Dickey et al. 1994; Mebold et al. 1997; Marx-Zimmer et al. 1998). Apparently, the population of cool HI clouds reaches kinetic gas temperatures down to as low as 10 or 20 K. These clouds may play an important role in the formation of stars in the LMC. We studied the association between the cool atomic gas and molecular gas in the LMC by 12CO(1–0) line observations in directions of cool HI clouds using the 15-m Swedish-ESO Submillimetre Telescope (SEST).

scholarly journals The molecular gas content in a protocluster at z = 17: Star formation and AGN feedback

2019 ◽  
Vol 15 (S352) ◽  
pp. 168-170
Author(s):  
Q. D’Amato ◽  
I. Prandoni ◽  
R. Gilli ◽  
M. Massardi ◽  
E. Liuzzo ◽  
...  
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Gas Content ◽  
Molecular Gas ◽  
Star Forming ◽  
Physical Conditions ◽  
Radio Jets ◽  
Multi Wavelength ◽  
Data Coverage

AbstractA large-scale structure has been recently discovered at z = 1.7, around a powerful FRII radio galaxy. Eight Star Forming Galaxies (SFGs) have been discovered within Δ z ≍ 0.0095 and at < 1 Mpc from the FRII, indicating that this is a signpost of a protocluster. Furthermore, a significant X-ray diffuse emission overlapping the Eastern lobe of the FRII has been detected. Protoclusters are the ideal targets to investigate the complex assembly processes leading to the formation of local galaxy clusters. We will exploit new ALMA CO(2-1) observations (PI: R. Gilli) of the entire region around the FRII galaxy to trace the molecular gas content, in order to discover new protocluster members. Coupling these measurements with the multi-wavelength data coverage available for this field, we aim at placing constrains on the physical conditions in which star formation occurs, and ultimately infer the role of the radio jets in triggering it.

scholarly journals Gas and star formation from HD and dust emission in a strongly lensed galaxy

2020 ◽  
Vol 498 (3) ◽  
pp. 4109-4118
Author(s):  
G C Jones ◽  
R Maiolino ◽  
P Caselli ◽  
S Carniani
Keyword(s):  
Star Formation ◽  
Conversion Factor ◽  
High Redshift ◽  
Spectral Energy Distribution ◽  
Formation Rate ◽  
Gas Content ◽  
Spectral Energy ◽  
Molecular Gas ◽  
Co Conversion ◽  
Single Temperature

ABSTRACT The molecular gas content of high-redshift galaxies is a highly sought-after property. However, H2 is not directly observable in most environments, so its mass is probed through other emission lines (e.g. CO, [C i], [C ii]), or through a gas-to-dust ratio. Each of these methods depends on several assumptions, and are best used in parallel. In this work, we extend an additional molecular gas tracer to high-redshift studies by observing hydrogen deuteride (HD) emission in the strongly lensed z = 5.656 galaxy SPT0346−52 with ALMA. While no HD(1–0) emission is detected, we are able to place an upper limit on the gas mass of $\rm M_{H_2}\lt 6.4\times 10^{11}\, M_{\odot }$. This is used to find a limit on the $L^{\prime }_{\mathrm{ CO}}$ conversion factor of      $\rm \alpha _{CO}\lt 5.8\,M_{\odot}(K\,km\,s^{-1}\,pc^2)^{-1}$. In addition, we construct the most complete spectral energy distribution of this source to date, and fit it with a single-temperature modified blackbody using the nested sampling code multinest, yielding a best-fitting dust mass Mdust = 108.92 ± 0.02 M⊙, dust temperature 78.6 ± 0.5 K, dust emissivity spectral index β = 1.81 ± 0.03, and star formation rate SFR = 3800 ± 100 M⊙ yr−1. Using the continuum flux densities to estimate the total gas mass of the source, we find   $\rm M_{H_2}\lt 2.4\times 10^{11}\, M_{\odot }$ , assuming subsolar metallicity. This implies a CO conversion factor of αCO &lt; 2.2, which is between the standard values for MW-like galaxies and starbursts. These properties confirm that SPT0346−52 is a heavily starbursting, gas-rich galaxy.

scholarly journals The implications of the surprising existence of a large, massive CO disk in a distant protocluster

2017 ◽  
Vol 608 ◽  
pp. A48 ◽  
Author(s):  
H. Dannerbauer ◽  
M. D. Lehnert ◽  
B. Emonts ◽  
B. Ziegler ◽  
B. Altieri ◽  
...  
Keyword(s):  
Star Formation ◽  
High Redshift ◽  
Formation Rate ◽  
Optical Emission ◽  
Rotating Disk ◽  
Major Axis ◽  
Gas Content ◽  
Molecular Gas ◽  
Star Forming ◽  
Co Emission

It is not yet known if the properties of molecular gas in distant protocluster galaxies are significantly affected by their environment as galaxies are in local clusters. Through a deep, 64 h of effective on-source integration with the Australian Telescope Compact Array (ATCA), we discovered a massive, Mmol = 2.0 ± 0.2× 1011 M⊙, extended, ~40 kpc, CO(1–0)-emitting disk in the protocluster surrounding the radio galaxy, MRC 1138−262. The galaxy, at zCO = 2.1478, is a clumpy, massive disk galaxy, M∗ ~ 5 × 1011 M⊙, which lies 250 kpc in projection from MRC 1138−262 and is a known Hα emitter, named HAE229. This source has a molecular gas fraction of ~30%. The CO emission has a kinematic gradient along its major axis, centered on the highest surface brightness rest-frame optical emission, consistent with HAE229 being a rotating disk. Surprisingly, a significant fraction of the CO emission lies outside of the UV/optical emission. In spite of this, HAE229 follows the same relation between star-formation rate and molecular gas mass as normal field galaxies. HAE229 is the first CO(1–0) detection of an ordinary, star-forming galaxy in a protocluster. We compare a sample of cluster members at z > 0.4 thatare detected in low-order CO transitions, with a similar sample of sources drawn from the field. We confirm findings that the CO-luminosity and full-width at half maximum are correlated in starbursts and show that this relation is valid for normal high-z galaxies as well as for those in overdensities. We do not find a clear dichotomy in the integrated Schmidt-Kennicutt relation for protocluster and field galaxies. Our results suggest that environment does not have an impact on the “star-formation efficiency” or the molecular gas content of high-redshift galaxies. Not finding any environmental dependence in these characteristics, especially for such an extended CO disk, suggests that environmentally-specific processes such as ram pressure stripping do not operate efficiently in (proto)clusters.

scholarly journals Spatially resolved molecular gas properties of host galaxy of Type I superluminous supernova SN 2017egm

2020 ◽  
Vol 72 (4) ◽  
Author(s):  
Bunyo Hatsukade ◽  
Kana Morokuma-Matsui ◽  
Masao Hayashi ◽  
Nozomu Tominaga ◽  
Yoichi Tamura ◽  
...  
Keyword(s):  
Star Formation ◽  
Column Density ◽  
Formation Rate ◽  
Host Galaxy ◽  
Molecular Gas ◽  
Type I ◽  
Type Ii ◽  
Star Forming ◽  
Spatially Resolved ◽  
Normal Star

Abstract We present the results of CO(1–0) observations of the host galaxy of a Type I superluminous supernova (SLSN-I), SN 2017egm, one of the closest SLSNe-I at z = 0.03063, by using the Atacama Large Millimeter/submillimeter Array. The molecular gas mass of the host galaxy is Mgas = (4.8 ± 0.3) × 109 M⊙, placing it on the sequence of normal star-forming galaxies in an Mgas–star-formation rate (SFR) plane. The molecular hydrogen column density at the location of SN 2017egm is higher than that of the Type II SN PTF10bgl, which is also located in the same host galaxy, and those of other Type II and Ia SNe located in different galaxies, suggesting that SLSNe-I have a preference for a dense molecular gas environment. On the other hand, the column density at the location of SN 2017egm is comparable to those of Type Ibc SNe. The surface densities of molecular gas and the SFR at the location of SN 2017egm are consistent with those of spatially resolved local star-forming galaxies and follow the Schmidt–Kennicutt relation. These facts suggest that SLSNe-I can occur in environments with the same star-formation mechanism as in normal star-forming galaxies.

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