Monday, 05-19-2014 Extended [CII

Emission in Local Luminous Infrared Galaxies]‚Äč
Extended [CII] Emission in Local Luminous Infrared Galaxies
Authors: T. Diaz-Santos, L. Armus, V. Charmandaris, G. Stacey, E. J. Murphy, S. Haan, S. Stierwalt, S. Malhotra, P. Appleton, H. Inami, G. E. Magdis, D. Elbaz, A. S. Evans, J. M. Mazzarella, J. A. Surace, P. P. van der Werf, C. K. Xu, N. Lu, R. Meijerink, J. H. Howell, A. O. Petric, S. Veilleux, D. B. Sanders
(Submitted on 15 May 2014)

Abstract: We present Herschel/PACS observations of extended [CII]157.7{\mu}m line emission detected on ~ 1 – 10 kpc scales in 60 local luminous infrared galaxies (LIRGs) from the Great Observatories All-sky LIRG Survey (GOALS). We find that most of the extra-nuclear emission show [CII]/FIR ratios >~ 4 x 10^-3, larger than the mean ratio seen in the nuclei, and similar to those found in the extended disks of normal star-forming galaxies and the diffuse inter-stellar medium (ISM) of our Galaxy. The [CII] “deficits” found in the most luminous local LIRGs are therefore restricted to their nuclei. There is a trend for LIRGs with warmer nuclei to show larger differences between their nuclear and extra-nuclear [CII]/FIR ratios. We find an anti-correlation between [CII]/FIR and the luminosity surface density, {\Sigma}_IR, for the extended emission in the spatially-resolved galaxies. However, there is an offset between this trend and that found for the LIRG nuclei. We use this offset to derive a beam filling-factor for the star-forming regions within the LIRG disks of ~ 6 % relative to their nuclei. We confront the observed trend to photo-dissociation region (PDR) models and find that the slope of the correlation is much shallower than the model predictions. Finally, we compare the correlation found between [CII]/FIR and {\Sigma}_IR with measurements of high-redshift starbursting IR-luminous galaxies.

Comments: Accepted for publication in ApJ Letters. 5 pages, 2 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:1405.3983 [astro-ph.GA]
(or arXiv:1405.3983v1 [astro-ph.GA] for this version)

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Weekend Reading – May 16, 2014

In the interest of motivating new thoughts in my head I’ve decided to prioritize actually reading something. I’ve been keeping a list of papers that I intended to read, largely from Hot Topics. I thought I would post them incase someone else thought they were worth a read too. Perhaps these might lead to some useful discussion in the coming week.

Molecular Cloud Scale Star formation in NGC300

Wide-field 12CO(J=1-0) Imaging of the Nearby Barred Galaxy M83 with NMA and Nobeyema 45-m telescope: Molecular Gas Kinematics and Star Formation Along the Bar

Enhancement of CO 3-2/1-0 ratios and Star Formation Efficiencies in Supergiant HII Regions

Modeling [CI] emission from turbulent molecular clouds


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Monday Nov. 4, 2013

Three papers today. First, the environment dependence of SF in the center of IC342 looks at Xco and what causes it to vary. The abstract indicates that Xco varies with sigma H2, and that it agrees with theoretical predictions, so they must be claiming a decrease in 12CO optical depth do to the of molecular gas.

The second a paper is on JD’s favorite topic, Cosmic Rays. How Cosmic Rays couple to a multiphase ISM is evaluated, with a focus on where the energy is deposited. They end up finding that the CR energy injection rate (a function of density) ends up being fairly consistent with the average density of the multiphase ISM, as long as you don’t get too dense or to close to a GMC, or have very tangled B fields. At that point it should CR energy injection rates should increase significant, but I’ll have to read the paper to see by how much.

Environmental Dependence of Star Formation Law in the Disk and Center of IC 342 Authors: Hsi-An Pan (1 and 2), Nario Kuno (1 and 2), Akihiko Hirota (2) ((1) Department of Astronomical Science, The Graduate University for Advanced Studies, Kanagawa, Japan, (2) Nobeyama Radio Observatory of NAOJ, Nagano, Japan)
(Submitted on 1 Nov 2013)

Abstract: The Kennicutt-Schmidt (K–S) law in IC 342 is examined using the 12CO-to-H2 conversion factor (Xco,v), which depends on the metallicity and CO intensity. Additionally, an optically thin 13CO (1-0) is also independently used to analyze the K–S law. Xco,v is two to three times lower than the Galactic standard Xco in the galactic center and approximately two times higher than Xco at the disk. The surface densities of molecular gas (Sigma_H2) derived from 12CO and 13CO are consistent at the environment in a high-Sigma_H2 region. By comparing the K-S law in the disk and the central regions of IC 342, we found that the power law index of K-S law (N) increases toward the central region. Furthermore, the dependence of N on Sigma_H2 is observed. Specifically, N increases with Sigma_H2. The derived N in this work and previous observations are consistent with the implication that star formation is likely triggered by gravitational instability in the disk (low-Sigma_H2 region) of IC 342 and both gravitational instability and cloud-cloud collisions in the central region (high-Sigma_H2 regime). In addition, the increasing N toward the high-Sigma_H2 domain also matches the theoretical prediction regarding the properties of giant molecular clouds. The results of IC 342 are supported by the same analysis of other nearby galaxies.

Cosmic Ray Sampling of a Clumpy Interstellar Medium
Authors: Erin Boettcher, Ellen G. Zweibel, Tova M. Yoast-Hull, J. S. Gallagher III
(Submitted on 31 Oct 2013)

Abstract: How cosmic rays sample the multi-phase interstellar medium (ISM) in starburst galaxies has important implications for many science goals, including evaluating the cosmic ray calorimeter model for these systems, predicting their neutrino fluxes, and modeling their winds. Here, we use Monte Carlo simulations to study cosmic ray sampling of a simple, two-phase ISM under conditions similar to those of the prototypical starburst galaxy M82. The assumption that cosmic rays sample the mean density of the ISM in the starburst region is assessed over a multi-dimensional parameter space where we vary the number of molecular clouds, the galactic wind speed, the extent to which the magnetic field is tangled, and the cosmic ray injection mechanism. We evaluate the ratio of the emissivity from pion production in molecular clouds to the emissivity that would be observed if the cosmic rays sampled the mean density, and seek areas of parameter space where this ratio differs significantly from unity. The assumption that cosmic rays sample the mean density holds over much of parameter space; however, this assumption begins to break down for high cloud density, injection close to the clouds, and a very tangled magnetic field. We conclude by evaluating the extent to which our simulated starburst region behaves as a proton calorimeter and constructing the time-dependent spectrum of a burst of cosmic rays.

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Astronomers Discover Star-Forming Galaxy Fueled by Primordial Hydrogen | Astronomy |

Very cool:

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Thursday September 26th, 2013

Cold dust but warm gas in the unusual elliptical galaxy NGC 4125

C. D. Wilson, A. Cridland, K. Foyle, T. J. Parkin, E. Mentuch Cooper, H. Roussel, M. Sauvage, M. W. L. Smith, M. Baes,G. Bendo, M. Boquien, A. Boselli, L. Ciesla, D. L. Clements, A. Cooray, I. De Looze, M. Galametz, W. Gear, V. Lebouteiller, S. Madden, M. Pereira-Santaella, A. Remy-Ruyer
(Submitted on 24 Sep 2013)

Data from the Herschel Space Observatory have revealed an unusual elliptical galaxy, NGC 4125, which has strong and extended submillimeter emission from cold dust but only very strict upper limits to its CO and HI emission. Depending on the dust emissivity, the total dust mass is 2-5×10^6 Msun. While the neutral gas-to-dust mass ratio is extremely low (< 12-30), including the ionized gas traced by [CII] emission raises this limit to < 39-100. The dust emission follows a similar r^{1/4} profile to the stellar light and the dust to stellar mass ratio is towards the high end of what is found in nearby elliptical galaxies. We suggest that NGC 4125 is currently in an unusual phase where evolved stars produced in a merger-triggered burst of star formation are pumping large amounts of gas and dust into the interstellar medium. In this scenario, the low neutral gas-to-dust mass ratio is explained by the gas being heated to temperatures >= 10^4 K faster than the dust is evaporated. If galaxies like NGC 4125, where the far-infrared emission does not trace neutral gas in the usual manner, are common at higher redshift, this could have significant implications for our understanding of high redshift galaxies and galaxy evolution.

Comments: Accepted to ApJ Letters
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:1309.6338 [astro-ph.CO]
(or arXiv:1309.6338v1 [astro-ph.CO] for this version)
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19 September, 2013 13:59

Low Masses and High Redshifts: The Evolution of the Mass-Metallicity Relation

Alaina Henry, Claudia Scarlata, Alberto Dominguez, Matthew Malkan, Crystal L. Martin, Brian Siana, Hakim Atek, Alejandro G. Bedregal, James W. Colbert, Marc Rafelski, Nathaniel Ross,Harry Teplitz, Andrew J. Bunker, Alan Dressler, Nimish Hathi, Daniel Masters, Patrick McCarthy, Amber Straughn
(Submitted on 17 Sep 2013)

We present the first robust measurement of the high redshift mass-metallicity (MZ) relation at 10^{8}< M/M_{\sun} < 10^{10}, obtained by stacking spectra of 83 emission-line galaxies with secure redshifts between 1.3 < z < 2.3. For these redshifts, infrared grism spectroscopy with the Hubble Space Telescope Wide Field Camera 3 is sensitive to the R23 metallicity diagnostic: ([OII]3726,3729 + [OIII] 4959,5007)/H\beta. Using spectra stacked in four mass quartiles, we find a MZ relation that declines significantly with decreasing mass, extending from 12+log(O/H) = 8.8 at M=10^{9.8} M_{\sun} to 12+log(O/H)= 8.2 at M=10^{8.2} M_{\sun}. After correcting for systematic offsets between metallicity indicators, we compare our MZ relation to measurements from the stacked spectra of galaxies with M>10^{9.5} M_{\sun} and z~2.3. Within the statistical uncertainties, our MZ relation agrees with the z~2.3 result, particularly since our somewhat higher metallicities (by around 0.1 dex) are qualitatively consistent with the lower mean redshift z=1.76 of our sample. For the masses probed by our data, the MZ relation shows a steep slope which is suggestive of feedback from energy-driven winds, and a cosmological downsizing evolution where high mass galaxies reach the local MZ relation at earlier times. In addition, we show that our sample falls on an extrapolation of the star-forming main sequence (the SFR-M_{*} relation) at this redshift. This result indicates that grism emission-line selected samples do not have preferentially high SFRs. Finally, we report no evidence for evolution of the mass-metallicity-SFR plane; our stack-averaged measurements show excellent agreement with the local relation.

Comments: Accepted for publication in ApJ Letters
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
Cite as: arXiv:1309.4458 [astro-ph.CO]
(or arXiv:1309.4458v1 [astro-ph.CO] for this version)

The role of galaxy interaction in the SFR-M relation: characterizing morphological properties of Herschel-selected galaxies at 0.2<z<1.5

Chao-Ling Hung (1), David B. Sanders (1), Caitlin M. Casey (1), Nicholas Lee (1), Joshua E. Barnes (1), Peter Capak (2), Jeyhan S. Kartaltepe (3), Michael Koss (1), Kirsten L. Larson (1),Emeric Le Floc’h (4), Kelly Lockhart (1), Allison W. S. Man (5,1), Andrew W. Mann (1), Laurie Riguccini (6,7), Nicholas Scoville (8), Myrto Symeonidis (9,10) ((1) IfA Hawaii, (2) SSC Caltech, (3) NOAO, (4) CEA-Saclay, (5) DARK Denmark, (6) NASA Ames, (7) BAER, (8) Caltech, (9) Sussex, (10) UCL)
(Submitted on 17 Sep 2013)

Galaxy interactions/mergers have been shown to dominate the population of IR luminous galaxies (log(LIR)>11.6Lsun) in the local Universe (z<0.25). Recent studies based on the relation between galaxies’ star formation rates and stellar mass (the SFR-M relation or the galaxy main sequence (MS)) have suggested that galaxy interaction/mergers may only become significant when galaxies fall well above the galaxy MS. Since the typical SFR at given M increases with redshift, the existence of galaxy MS implies that massive, IR-luminous galaxies at high-z may not necessarily be driven by galaxy interactions. We examine the role of galaxy interactions in the SFR-M relation by carrying out a morphological analysis of 2084 Herschel-selected galaxies at 0.2 < z < 1.5 in the COSMOS field. Herschel-PACS and -SPIRE observations covering the full 2-deg^2 COSMOS field provide one of the largest far-IR selected samples of high-redshift galaxies with well-determined redshifts to date, with sufficient sensitivity at z ~ 1, to sample objects lying on and above the galaxy MS. Using a detailed visual classification scheme, we show that the fraction of "disk galaxies" decreases and the fraction of "irregular" galaxies increases systematically with increasing LIR out to z ~ 1.5 and z ~ 1.0, respectively. At log(LIR) > 11.5 Lsun, >50% of the objects show evident features of strongly interacting/merger systems, where this percentage is similar to the studies of local IR-luminous galaxies. The fraction of interacting/merger systems also systematically increases with the deviation from the SFR-M relation, supporting the view that galaxies fall above the MS are more dominated by mergers than the MS galaxies. Meanwhile, we find that ~18% of massive IR-luminous MS galaxies are classified as interacting systems, where this population may not evolve through the evolutionary track predicted by a simple gas exhaustion model.

Comments: 14 pages, 11 figures, ApJ accepted
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1309.4459 [astro-ph.CO]
(or arXiv:1309.4459v1 [astro-ph.CO] for this version)
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Paper to Read for Group Meeting

Hi all, here’s the X(CO) review by Bolatto, Wolfire and Leroy that we’re going to talk about for next week’s group meeting. -Alison

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