Thursday September 5th, 2013

The first author can only be trusted so far. For one, Section 2.3 fails to mention a certain contributing grad student that helped with the NGC628 IRS data. For another, he’s short and his hair is too awesome.

He’s dead to me.
</joke>

Our very own Kevin Croxall tackles the annoying issues surrounding chemical abundances using NGC628. This is certainly worth your time!

Towards A Removal of Temperature Dependencies from Abundance Determinations

Kevin V. Croxall, J.D. Smith, B.R. Brandl, B. A. Groves, R. C. Kennicutt, K. Kreckel, B. D. Johnson, E. Pellegrini, K. M. Sandstrom, F. Walter, L. Armus, P. Beirao, D. Calzetti,D.A. Dale, M. Galametz, J. L. Hinz, L. K. Hunt, J. Koda, E. Schinnerer
(Submitted on 3 Sep 2013)

The metal content of a galaxy is a key property for distinguishing between viable galaxy evolutionary scenarios, and it strongly influences many of the physical processes in the interstellar medium. An absolute and robust determination of extragalactic metallicities is essential in constraining models of chemical enrichment and chemical evolution, however, current gas phase abundance determinations from optical fine-structure lines are uncertain to 0.8 dex as conversion of these optical line fluxes to abundances is strongly dependent on the electron temperature of the ionized gas. In contrast, the far-IR emission lines can be used to derive an O++ abundance that is relatively insensitive to temperature, while the ratio of the optical to far-IR lines provides a consistent temperature to be used in the derivation of an O$^+$ abundance. We present observations of the [O III] 88 \micron\ fine-structure line in NGC 628 that were obtained as part of the KINGFISH program. These data are combined with optical IFU data to derive oxygen abundances for seven HII regions. We find the abundance of these regions to all lie between the high and low values of strong line calibrations and in agreement with estimates that assume temperature fluctuations are present in the HII regions.

Comments: 12 pages, 7 Figures, 3 Tables, 6 online-only figures, accepted for publication in ApJ
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1309.0817 [astro-ph.CO]
(or arXiv:1309.0817v1 [astro-ph.CO] for this version)
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Thursday August 29th, 2013

Recently in our circle we have been repeatedly discussing that the centers of galaxies are typically dominated by older stellar populations, resulting in a very ‘red’ energy distribution. However, Dewitt et. al. uses near-infrared spectroscopy to identify three x-ray sources near the galactic center as high mass stars/binaries.

The next paper by Giardi et. al. suggests that the contributions of Thermally Pulsating Asymptotic Giant Branch (TP-AGB) in cluster models may be overestimated by a factor of two. Could this possibly have implications for dust production models relying on such stars? Either way, this paper is somewhat amusing for its rather colorful language.

Finally, Howard et. al. presents some [OI] and [CII] line data from Herschel on protoplanetary disks.

Three New Galactic Center X-ray Sources Identified with Near-Infrared Spectroscopy

Curtis DeWitt, Reba M. Bandyopadhyay, Stephen S. Eikenberry, Kris Sellgren, Robert Blum, Knut Olsen, Franz E. Bauer, Ata Sarajedini
(Submitted on 28 Aug 2013)

We have conducted a near-infrared spectroscopic survey of 47 candidate counterparts to X-ray sources discovered by the Chandra X-ray Observatory near the Galactic Center (GC). Though a significant number of these astrometric matches are likely to be spurious, we sought out spectral characteristics of active stars and interacting binaries, such as hot, massive spectral types or emission lines in order to corroborate the X-ray activity and certify the authenticity of the match. We present three new spectroscopic identifications, including a Be high mass X-ray binary (HMXB) or a gamma Cassiopeiae (Cas) system, a symbiotic X-ray binary and an O-type star of unknown luminosity class. The Be HMXB/gamma Cas system and the symbiotic X-ray binary are the first of their classes to be spectroscopically identified in the GC region.

Comments: 33 pages, 12 figures, AJ accepted
Subjects: Galaxy Astrophysics (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)
Cite as: arXiv:1308.6252 [astro-ph.GA]
(or arXiv:1308.6252v1 [astro-ph.GA] for this version)

The insidious boosting of TP-AGB stars in intermediate-age Magellanic Cloud clusters

Leo Girardi, Paola Marigo, Alessandro Bressan, Philip Rosenfield
(Submitted on 28 Aug 2013)

(Abridged) In the recent controversy about the role of TP-AGB stars in evolutionary population synthesis (EPS) models of galaxies, one particular aspect is puzzling: TP-AGB models aimed at reproducing the lifetimes and integrated fluxes of the TP-AGB phase in Magellanic Cloud (MC) clusters, when incorporated into EPS models, are found to overestimate the TP-AGB contribution in resolved star counts and integrated spectra of galaxies. In this paper, we call attention to a particular evolutionary aspect that in all probability is the main cause of this conundrum. As soon as stellar populations intercept the ages at which RGB stars first appear, a sudden change in the lifetime of the core He-burning phase causes a temporary boost in the production rate of subsequent evolutionary phases, including the TP-AGB. For a timespan of about 0.1 Gyr, triple TP-AGB branches develop at slightly different initial masses, causing their frequency and contribution to the integrated luminosity of the stellar population to increase by a factor of 2. The boost occurs just in the proximity of the expected peak in the TP-AGB lifetimes, and for ages of 1.6 Gyr. Coincidently, this relatively narrow age interval happens to contain the few very massive MC clusters that host most of the TP-AGB stars used to constrain stellar evolution and EPS models. This concomitance makes the AGB-boosting particularly insidious in the context of present EPS models. The effect brings about three main consequences. (1) Present estimates of the TP-AGB contribution to the integrated light of galaxies derived from MC clusters, are biased towards too large values. (2) The relative TP-AGB contribution of single-burst populations falling in this critical age range cannot be accurately derived by the fuel consumption theorem. (3) A careful revision of AGB star populations in intermediate-age MC clusters is urgently demanded.

Comments: ApJ accepted, 12 pages
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:1308.6088 [astro-ph.SR]
(or arXiv:1308.6088v1 [astro-ph.SR] for this version)

Herschel/PACS Survey of protoplanetary disks in Taurus/Auriga — Observations of [OI] and [CII], and far infrared continuum

Christian D. Howard (1,2), Göran Sandell (1), William D.Vacca (1), Gaspard Duchêne (3,4), Geoffrey Mathews (5,6), Jean-Charles Augereau (4), David Barrado (7,8),William R. F.Dent (9), Carlos Eiroa (10), Carol Grady (11,12,13), Inga Kamp (14), Gwendolyn Meeus (10), Francois Ménard (4,15), Christophe Pinte (4), Linda Podio (4),Pablo Riviere-Marichalar (7), Aki Roberge (11), Wing-Fai Thi (4), Silvia Vicente (14), Jonathan P. Williams (6) ((1) SOFIA-USRA, NASA Ames Research Center (2) Google (3) UC Berkeley (4) UJF-Grenoble (5) Leiden Observatory (6) IfA, University of Hawaii (7) Centro de Astrobiologia, ESAC (8) Calar Alto Observatory (9) ALMA SCO (10) Dep de Fisica Theoretica, UAM (11) Exoplanets and Stellar Astrophys. Lab, NASA Goddard (12) Eureca Scientific (13) Kapteyn Astronomical Institute (14) UMI-FCA, France and Univ. de Chile)
(Submitted on 28 Aug 2013)

The Herschel Space Observatory was used to observe ~ 120 pre-main-sequence stars in Taurus as part of the GASPS Open Time Key project. PACS was used to measure the continuum as well as several gas tracers such as [OI] 63 \mu m, [OI] 145 \mu m, [CII] 158 \mu m, OH, H2O and CO. The strongest line seen is [OI] at 63 \mu m. We find a clear correlation between the strength of the [OI] 63 \mu m line and the 63 \mu m continuum for disk sources. In outflow sources, the line emission can be up to 20 times stronger than in disk sources, suggesting that the line emission is dominated by the outflow. The tight correlation seen for disk sources suggests that the emission arises from the inner disk ($<$ 50 AU) and lower surface layers of the disk where the gas and dust are coupled. The [OI] 63 \mu m is fainter in transitional stars than in normal Class II disks. Simple SED models indicate that the dust responsible for the continuum emission is colder in these disks, leading to weaker line emission. [CII] 158 \mu m emission is only detected in strong outflow sources. The observed line ratios of [OI] 63 \mu m to [OI] 145 \mu m are in the regime where we are insensitive to the gas-to-dust ratio, neither can we discriminate between shock or PDR emission. We detect no Class III object in [OI] 63 \mu m and only three in continuum, at least one of which is a candidate debris disk.

Comments: 84 pages, 14 figures, 5 tables. Accepted by ApJ
Subjects: Galaxy Astrophysics (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:1308.6019 [astro-ph.GA]
(or arXiv:1308.6019v1 [astro-ph.GA] for this version)

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Fri 8/23

Two MIR color selected evolutionary studies, on hot dust, and radio AGN.

JD

Hot-Dust (690K) Luminosity Density and its Evolution in the last 7.5Gyr

Hugo Messias, Bahram Mobasher, José Manuel Afonso
(Submitted on 21 Aug 2013)

[Abridged] We study the contribution of hot-dust to the luminosity density of galaxies and its evolution with cosmic time. Using the Spitzer-IRAC data in the COSMOS field, we estimate the contribution from hot-dust at rest-frame 4.2um (from ~0 < z < ~0.2 up to ~0.5 < z < ~0.9). This wavelength corresponds to black-body temperature of ~690K. The contribution due to stellar emission is estimated from the rest-frame 1.6um luminosity (assumed to result from stellar emission alone) and subtracted from the mid-infrared luminosity of galaxies to measure hot-dust emission. In order to attempt the study of the 3.3um-PAH feature, we use the rest-frame 4.2um to infer the hot-dust flux at 3.3um. This study is performed for different spectral types of galaxies: early-type, late-type, starburst, and IR-selected AGN. We find that: (a) the decrease of the hot-dust luminosity density since ~0.5 < z < ~1 is steeper (by at least ~0.5dex) compared to that of the cold-dust, giving support to the scenario where galaxy obscuration increases with redshift, as already proposed in the literature; (b) hot-dust and PAH emission evolution seems to be correlated with stellar mass, where rest-frame 1.6um luminous non-AGN galaxies (i.e., massive systems) show a stronger decrement (with decreasing redshift) in hot-dust and PAH emission than the less luminous (less massive) non-AGN galaxies; (c) despite comprising < ~3% of the total sample, AGN contribute as much as a third to the hot-dust luminosity density at z < 1 and clearly dominate the bright-end of the total hot-dust Luminosity Density Function at ~0.5 < z < ~0.9; (d) the average dust-to-total luminosity ratio increases with redshift, while PAH-to-total luminosity ratio remains fairly constant; (e) at M_1.6 > -25, the dust-to-total and PAH-to-total luminosity ratios increase with decreasing luminosity, but deeper data is required to confirm this result.

Comments: Accepted on The Astrophysical Journal on August 20th 2013, emulateapj, 14 pages, 16 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1308.4683 [astro-ph.CO]

The WISE properties of complete samples of radio-loud AGN

G. Gurkan, M. J. Hardcastle, M. J. Jarvis
(Submitted on 22 Aug 2013)

We present an analysis of four complete samples of radio-loud AGN (3CRR, 2Jy, 6CE and 7CE) using near- and mid-IR data taken by the Wide-Field Infrared Survey Explorer (WISE). The combined sample consists of 79 quasars and 273 radio galaxies, and covers a redshift range 0.003<z<3.395. The dichotomy in the mid-IR properties of low- and high-excitation radio galaxies (LERGs – HERGs) is analysed for the first time using large complete samples. Our results demonstrate that a division in the accretion modes of LERGs and HERGs clearly stands out in the mid-IR-radio plane (L_(22 \mu m) = 5×10^(43) erg s^(-1)). This means that WISE data can be effectively used to diagnose accretion modes in radio-loud AGN. The mid-IR properties of all objects were analysed to test the unification between quasars and radio galaxies, consistent with earlier work and we argue that smooth torus models best reproduce the observation. Quasars are found to have higher mid-IR luminosities than radio galaxies. We also studied all the sources in the near-IR to gain insights into evolution of AGN host galaxies. A relation found between the near-IR luminosity and redshift, well-known in the near-IR, is apparent in the two near-IR WISE bands, supporting the idea that radio sources are hosted by massive elliptical galaxies that formed their stars at high redshifts and evolved passively thereafter. Evaluation of the positions of the sample objects in WISE colour-colour diagrams shows that widely used WISE colour cuts are not completely reliable in selecting AGN.

Comments: 13 pages, 10 figures, submitted to MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1308.4843 [astro-ph.CO]
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Mon. 8/20/2013

This is Tera Parkin’s paper from Christine Wilson’s group on M51. This will be an important paper from the point of view of setting ISM conditions in galaxies. This work makes use of PACS and SPIRE data, and is complementary to many of the research avenues of KINGFISH and Beyond the Peak.

Regional variations in the dense gas heating and cooling in M51 from Herschel far-infrared spectroscopyAuthors: T. J. Parkin, C. D. Wilson, M. R. P. Schirm, M. Baes, M. Boquien, A. Boselli, A. Cooray, D. Cormier, K. Foyle, O. L. Karczewski, V. Lebouteiller, I. de Looze, S. C. Madden, H. Roussel, M. Sauvage, L. Spinoglio
(Submitted on 16 Aug 2013)

Abstract: We present Herschel PACS and SPIRE spectroscopy of the most important far-infrared cooling lines in M51, [CII](158 \mu m), [NII](122 & 205 \mu m), [OI](63 and 145 \mu m) and [OIII](88 \mu m). We compare the observed flux of these lines with the predicted flux from a photon dominated region model to determine characteristics of the cold gas such as density, temperature and the far-ultraviolet radiation field, G_0, resolving details on physical scales of roughly 600 pc. We find an average [CII]/F_TIR of 4 x 10^{-3}, in agreement with previous studies of other galaxies. A pixel-by-pixel analysis of four distinct regions of M51 shows a radially decreasing trend in both the far-ultraviolet (FUV) radiation field, G_0 and the hydrogen density, n, peaking in the nucleus of the galaxy, then falling off out to the arm and interarm regions. We see for the first time that the FUV flux and gas density are similar in the differing environments of the arm and interarm regions, suggesting that the inherent physical properties of the molecular clouds in both regions are essentially the same.

Comments: 24 pages, 7 figures, 9 tables; accepted for publication in the Astrophysical Journal
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
Cite as: arXiv:1308.3702 [astro-ph.CO]
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Tuesday, 8/20/13

Just one paper today, possibly relevant for Adam’s post-starburst galaxies? – Alison

Title: A technique for estimation of starburst masses and ages in luminous compact galaxies
Authors: Parnovsky, S. L.; Izotova, I. Y.
Affiliation: AA(Astronomical Observatory of Taras Shevchenko Kyiv National University), AB(Astronomical Observatory of Taras Shevchenko Kyiv National University)
Publication: Astrophysics and Space Science, Online First (Ap&SS Homepage)
Publication Date: 07/2013
Origin: SPRINGER
Keywords: Galaxies: starburst, Galaxies: star formation, Galaxies
Abstract Copyright: (c) 2013: Springer Science+Business Media Dordrecht
DOI: 10.1007/s10509-013-1554-7
Bibliographic Code: 2013Ap&SS.tmp..286P

Abstract

We propose a technique for estimation of the mass m of the young stellar population and the starburst age T in luminous compact galaxies (LCGs). For this purpose we use LCG Hα emission line luminosities from the Sloan Digital Sky Survey (SDSS) spectra and Galaxy Evolution Explorer (GALEX) FUV and NUV continuum luminosities. The method is intended for quick estimation of m and T in large galaxy samples and does not require spectral energy distribution (SED) fitting. Estimated m and T for the sample of about 550 LCGs are compared with the same values derived from the SED fitting in the wavelength range λλ 3800-9200 Å. We obtain the average differences in logm and T of 0.27 and 0.87 Myr, respectively. This technique could be used for selection of galaxies with desired ranges of m and T or for reducing a range of parameter variations in SED fitting.

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Tuesday 8/13/13

A day off, I didn’t find any papers interesting enough to draw all of your attentions to… (Alison)

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Tuesday, 8/6/13

Just one paper today – and on [CI]! Shimajiri et al. have mapped the Orion-A molecular clouds in [CI] using the ASTE 10m telescope down in Chile. They find that the [CI] has a similar distribution to 12CO(1-0), but even more similar to 13CO(1-0) and C18O(1-0), which doesn’t fit well if the main route to C^0 is through photodissociation of CO. (Instead, C^0 must persist deep within molecular clouds. An option is perhaps some charge exchange reaction with sulphur…

Title: Extensive [CI] Mapping toward the Orion-A Molecular Cloud
Authors: Shimajiri, Yoshito; Sakai, Takeshi; Tsukagoshi, Takashi; Kitamura, Yoshimi; Momose, Munetake; Saito, Masao; Oshima, Tai; Kohno, Kotaro; Kawabe, Ryohei
Publication: eprint arXiv:1308.1036
Publication Date: 08/2013
Origin: ARXIV
Keywords: Astrophysics – Galaxy Astrophysics
Comment: 14 pages, 4 figures, 1 table, ApJL accepted for publication
Bibliographic Code: 2013arXiv1308.1036S

Abstract

We have carried out wide-field (0.17 degree^2) and high-angular resolution (21.3 arcsec ~ 0.04 pc) observations in [CI] line toward the Orion-A giant molecular cloud with the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope in the On-The-Fly (OTF) mode. Overall features of the [CI] emission are similar to those of the CO (1–0) emission in Shimajiri et al. 2011; the total intensity ratio of the [CI] to CO emission ranges from 0.05 to 0.2. The optical depth of the [CI] emission is found to be 0.1 — 0.75, suggesting optically thin emission. The column density of the [CI] emission is estimated to be (1.0 — 19) x 10^17 cm^-2. These results are consistent with the results of the previous [CI] observations with a low-angular resolution of 2.2 arcmin (e.g. Ikeda et al. 1999). In the nearly edge-on PDRs and their candidates of the Orion Bar, DLSF, M 43 Shell, and Region D, the distributions of the [CI] emission coincide with those of the CO emission, inconsistent with the prediction by the plane-parallel PDR model (Hollenbach & Tielens 1999). In addition, the [CI] distribution in the Orion A cloud is found to be more similar to those of the ^{13}CO (1–0), C^{18}O (1–0), and H^{13}CO^+ (1–0) lines than that of the CO (1–0) line, suggesting that the [CI] emission is not limited to the cloud surface, but is tracing the dense, inner parts of the cloud.

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