Monday 06/11/2012

Paper 1 :

Far-infrared Spectral Energy Distribution Fitting for Galaxies Near and Far

Caitlin M. Casey (IfA Hawai’i)
(Submitted on 7 Jun 2012)

Spectral Energy Distribution (SED) fitting in the far-infrared (FIR) is greatly limited by a dearth of data and an excess of free parameters – from galaxies’ dust composition, temperature, mass, orientation, opacity, to heating from AGN. This paper presents a simple FIR SED fitting technique joining a modified, single dust temperature greybody, representing the reprocessed starburst emission in the whole galaxy, to a mid-infrared powerlaw, which approximates hot-dust emission from AGN heating or clumpy, hot starbursting regions. This FIR SED can be used to measure infrared luminosities, dust temperatures and dust masses for both local and high-z galaxies with 3 to 10+ FIR photometric measurements.
This fitting method is compared to infrared template SEDs in the literature using photometric data on 65 local luminous and ultraluminous infrared galaxies, (U)LIRGs. Despite relying only on 2-4 free parameters, the coupled greybody/powerlaw SED fitting described here produces better fits to photometric measurements than best-fit literature template SEDs (with residuals a factor of ~2 lower). A mean emissivity index of beta=1.60+-0.38 and mid-infrared powerlaw slope of alpha=2.0+-0.5 is measured; the former agrees with the widely presumed emissivity index of beta=1.5 and the latter is indicative of an optically-thin dust medium with a shallow radial density profile, ~r^-0.5. Adopting characteristic dust temperature as the inverse wavelength where the SED peaks, dust temperatures ~25-45K are measured for local (U)LIRGs, ~5-15K colder than previous estimates using only simple greybodies. This comparative study highlights the impact of SED fitting assumptions on the measurement of physical properties such as infrared luminosity (and thereby infrared-based star formation rate), dust temperature and dust mass, for both local and high-redshift galaxies. [abridged]

Comments: 12 pages, 7 figures, MNRAS accepted
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1206.1595v1 [astro-ph.CO]

Paper 2 :

The JCMT Nearby Galaxies Legacy Survey VIII. CO data and the L(CO3-2)-L(FIR) correlation in the SINGS sample

C. D. Wilson, B. E. Warren, F. P. Israel, S. Serjeant, D. Attewell, G. J. Bendo, H. M. Butner, P. Chanial, D. L. Clements, J. Golding, V. Heesen, J. Irwin, J. Leech, H. E. Matthews, S. Muhle, A. M. J. Mortier, G. Petitpas, J. R. Sanchez-Gallego, E. Sinukoff, K. Shorten, B. K. Tan, R. P. J. Tilanus, A. Usero, M. Vaccari, T. Wiegert, M. Zhu,D. M. Alexander, P. Alexander, M. Azimlu, P. Barmby, C. Borys, R. Brar, C. Bridge, E. Brinks, S. Brooks, K. Coppin, S. Cote, P. Cote, S. Courteau, J. Davies, S. Eales, M. Fich, M. Hudson, D. H. Hughes, R. J. Ivison, J. H. Knapen, M. Page, T. J. Parkin, A. Pope, D. Rigopoulou, E. Rosolowsky, E. R. Seaquist, K. Spekkens, N. Tanvir,J. M. van der Hulst, P. van der Werf, C. Vlahakis, T. M. Webb, B. Weferling, G. J. White
(Submitted on 7 Jun 2012)

The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey (NGLS) comprises an HI-selected sample of 155 galaxies spanning all morphological types with distances less than 25 Mpc. We describe the scientific goals of the survey, the sample selection, and the observing strategy. We also present an atlas and analysis of the CO J=3-2 maps for the 47 galaxies in the NGLS which are also part of the Spitzer Infrared Nearby Galaxies Survey. We find a wide range of molecular gas mass fractions in the galaxies in this sample and explore the correlation of the far-infrared luminosity, which traces star formation, with the CO luminosity, which traces the molecular gas mass. By comparing the NGLS data with merging galaxies at low and high redshift which have also been observed in the CO J=3-2 line, we show that the correlation of far-infrared and CO luminosity shows a significant trend with luminosity. This trend is consistent with a molecular gas depletion time which is more than an order of magnitude faster in the merger galaxies than in nearby normal galaxies. We also find a strong correlation of the L(FIR)/L(CO3-2) ratio with the atomic to molecular gas mass ratio. This correlation suggests that some of the far-infrared emission originates from dust associated with atomic gas and that its contribution is particularly important in galaxies where most of the gas is in the atomic phase.

Comments: 37 pages, 107 figures; accepted for publication in MNRAS. Data and additional information are available at this http URL
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1206.1629v1 [astro-ph.CO]

Paper 3 :

Properties of the giant HII regions and bar in the nearby spiral galaxy NGC5430

É. Brière, S. Cantin, K. Spekkens
(Submitted on 8 Jun 2012)

In order to better understand the impact of the bar on the evolution of spiral galaxies, we measure the properties of giant HII regions and the bar in the SB(s)b galaxy NGC5430. We use two complementary data sets, both obtained at the Observatoire du Mont-M\’egantic: a hyperspectral data cube from the imaging Fourier transform spectrograph SpIOMM, and high-resolution spectra across the bar from a long-slit spectrograph. We flux-calibrate SpIOMM spectra for the first time, and produce H{\alpha} and [NII]{\lambda}6584\r{A} intensity maps from which we identify 51 giant HII regions in the spiral arms and bar. We evaluate the type of activity, the oxygen abundance and the age of the young populations contained in these giant HII regions and in the bar. Thus, we confirm that NGC5430 does not harbour a strong AGN, and that its Wolf-Rayet knot shows a pure HII region nature. We find no variation in abundance or age between the bar and spiral arms, nor as a function of galactocentric radius. These results are consistent with the hypothesis that a chemical mixing mechanism is at work in the galaxy’s disc to flatten the oxygen abundance gradient. Using the starburst99 model, we estimate the ages of the young populations, and again find no variations in age between the bar and the arms or as a function of radius. Instead, we find evidence for two galaxy-wide waves of star formation, about 7.1 Myr and 10.5 Myr ago. While the bar in NGC5430 is an obvious candidate to trigger these two episodes, it is not clear how the bar could induce widespread star formation on such a short time-scale.

Comments: 14 pages, 9 figures, 3 tables, accepted for publication in MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:1206.1656v1 [astro-ph.CO]

Paper 4 :

The NGC7771+NGC7770 Minor Merger: Harassing the Little One?

Almudena Alonso-Herrero (1), F. Fabian Rosales Ortega (2,3),Sebastian F. Sanchez (4,3), Robert C. Kennicutt (5), Miguel Pereira-Santaella (6), Angeles I. Diaz (2) ((1) IFCA, CSIC-UC, Spain, (2) Universidad Autonoma de Madrid, Spain, (3) Calar Alto, (4) IAA, CSIC, Spain, (5) Institute of Astronomy, Cambridge, UK, (6) Istituto di Astrofisica e Planetologia Spaziali, INAF-IAPS, Italy)
(Submitted on 8 Jun 2012)

Numerical simulations of minor mergers, typically having mass ratios greater than 3:1, predict little enhancement in the global star formation activity. However, these models also predict that the satellite galaxy is more susceptible to the effects of the interaction than the primary. We use optical integral field spectroscopy and deep optical imaging to study the NGC7771+NGC7770 interacting system (~10:1 stellar mass ratio) to test these predictions. We find that the satellite galaxy NGC7770 is currently experiencing a galaxy-wide starburst with most of the optical light being from young and post-starburst stellar populations(<1Gyr). This galaxy lies off of the local star-forming sequence for composite galaxies with an enhanced integrated specific star formation rate. We also detect in the outskirts of NGC7770 Halpha emitting gas filaments. This gas appears to have been stripped from one of the two galaxies and is being excited by shocks. All these results are consistent with a minor-merger induced episode(s) of star formation in NGC7770 after the first close passage. Such effects are not observed on the primary galaxy NGC7771.

Comments: Accepted for publication in MNRAS Letters
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1206.1686v1 [astro-ph.CO]
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