Thursday, February 8th, 2013

Kinematics of Star Clusters in M101

Lesley Simanton (1), Rupali Chandar (1), Bryan Miller (2) ((1) University of Toledo, (2) Gemini Observatory)
(Submitted on 6 Feb 2013)

We have identified a few thousand star clusters in the nearby, late-type spiral galaxy M101, including approximately 90 candidate ancient globular clusters (GCs), from multi-band Hubble Space Telescope (HST) images. We obtained follow-up low-resolution (R approximately 2000) optical spectroscopy from Gemini-GMOS for 43 total clusters, of which 18 are old GCs and 25 are young massive clusters (YMCs). We measure radial velocities for these clusters and find that, as expected, the YMCs rotate with the HI disk. The old GCs do not show any obvious evidence for rotation and have a much higher velocity dispersion than the YMCs, suggesting that the GCs in M101 are likely part of a stellar halo or thick disk.

Comments: 4 pages, 6 figures, To appear in conference proceedings of "Reading the book of globular clusters with the lens of stellar evolution"
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1302.1497 [astro-ph.CO]
(or arXiv:1302.1497v1 [astro-ph.CO] for this version)

GAMA/H-ATLAS: The Dust Opacity – Stellar Mass Surface Density Relation for Spiral Galaxies

M.W. Grootes, R.J. Tuffs, C.C. Popescu, B. Pastrav, E. Andrae, M. Gunawardhana, L.S. Kelvin, J. Liske, M. Seibert, E.N. Taylor, A.W. Graham, M. Baes, I.K. Baldry, N. Bourne, S. Brough, A. Cooray, A. Dariush, G. De Zotti, S.P. Driver, L. Dunne, H. Gomez, A.M. Hopkins, R. Hopwood, M. Jarvis, J. Loveday, S. Maddox,B.F. Madore, M.J. Michałowski, P. Norberg, H.R. Parkinson, M. Prescott, A.S.G. Robotham, D.J.B. Smith,D. Thomas, E. Valiante
(Submitted on 6 Feb 2013)

We report the discovery of a well-defined correlation between B-band face-on central optical depth due to dust, \tau^f_B, and the stellar mass surface density, \mu_{*}, of nearby (z < 0.13) spiral galaxies: log(\tau^f_B) = 1.12(+-0.11)log(\mu_{*}/M_sol kpc^2)-8.6(+-0.8). This relation was derived from a sample of spiral galaxies taken from the Galaxy and Mass Assembly (GAMA) survey and detected in the FIR/submm in the Herschel-ATLAS survey. Using a quantitative analysis of the NUV attenuation-inclination relation for complete samples of GAMA spirals categorized according to \mu_{*} we demonstrate that this correlation can be used to statistically correct for dust attenuation purely on the basis of optical photometry and S’ersic-profile morphological fits. Considered together with previously established empirical relationships between stellar mass, metallicity and gas mass, the near linearity and high constant of proportionality of the \tau^f_B-\mu_{*} relation disfavors a stellar origin for the bulk of refractory grains in spiral galaxies, instead being consistent with the existence of a ubiquitous and very rapid mechanism for the growth of dust in the ISM. We use the \tau^f_B-\mu_{*} relation in conjunction with the radiation transfer model for spiral galaxies of Popescu & Tuffs (2011) to derive intrinsic scaling relations between specific star formation rate (sSFR), stellar mass, and \mu_{*}, in which the attenuation of the UV light used to measure the SFR is corrected on an object-to-object basis. A marked reduction in scatter in these relations is achieved which is demonstrably due to correction of both the inclination-dependent and face-on components of attenuation. Our results are consistent with a picture of spiral galaxies in which most of the submm emission originates from grains residing in translucent structures, exposed to UV in the diffuse interstellar radiation field.

Comments: 21 pages, 9 figures, version as accepted by ApJ
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1302.1379 [astro-ph.CO]
(or arXiv:1302.1379v1 [astro-ph.CO] for this version)
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