Friday March 15

Beware the ides of March

Variation of Mid and Far-IR Luminosities among Early-Type Galaxies: Relation to Stellar Metallicity and Cold Dust

William G. Mathews, Pasquale Temi, Fabrizio Brighenti, Alexandre Amblard
(Submitted on 14 Mar 2013)

The Hubble morphological sequence from early to late galaxies corresponds to an increasing rate of specific star formation. The Hubble sequence also follows a banana-shaped correlation between 24 and 70 micron luminosities, both normalized with the K-band luminosity. We show that this correlation is significantly tightened if galaxies with central AGN emission are removed, but the cosmic scatter of elliptical galaxies in both 24 and 70 micron luminosities remains significant along the correlation. We find that the 24 micron variation among ellipticals correlates with stellar metallicity, reflecting emission from hot dust in winds from asymptotic giant branch stars of varying metallicity. Infrared surface brightness variations in elliptical galaxies indicate that the K – 24 color profile is U-shaped for reasons that are unclear. In some elliptical galaxies cold interstellar dust emitting at 70 and 160 microns may arise from recent gas-rich mergers. However, we argue that most of the large range of 70 micron luminosity in elliptical galaxies is due to dust transported from galactic cores by feedback events in (currently IR-quiet) active galactic nuclei. Cooler dusty gas naturally accumulates in the cores of elliptical galaxies due to dust-cooled local stellar mass loss and may accrete onto the central black hole, releasing energy. AGN-heated gas can transport dust in cores 5-10 kpc out into the hot gas atmospheres where it radiates extended 70 micron emission but is eventually destroyed by sputtering. This, and some modest star formation, defines a cycle of dust creation and destruction. Elliptical galaxies evidently undergo large transient excursions in the banana plot in times comparable to the sputtering time or AGN duty cycle, 10 Myrs. Normally regarded as passive, elliptical galaxies are the most active galaxies in the IR color-color correlation.

Comments: 17 pages, 8 figures, 2 tables, accepted for publication in ApJ
Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1303.3350 [astro-ph.GA]
(or arXiv:1303.3350v1 [astro-ph.GA] for this version)

Herschel/SPIRE Sub-millimeter Spectra of Local Active Galaxies

Miguel Pereira-Santaella, Luigi Spinoglio, Gemma Busquet, Christine D. Wilson, Jason Glenn, Kate G. Isaak, Julia Kamenetzky, Naseem Rangwala, Maximilien R. P. Schirm, Maarten Baes, Michael J. Barlow, Alessandro Boselli,Asantha Cooray, Diane Cormier
(Submitted on 14 Mar 2013)

We present the sub-millimeter spectra from 450 GHz to 1550 GHz of eleven nearby active galaxies observed with the SPIRE Fourier Transform Spectrometer (SPIRE/FTS) onboard Herschel. We detect CO transitions from J_up = 4 to 12, as well as the two [CI] fine structure lines at 492 and 809 GHz and the [NII] 461 GHz line. We used radiative transfer models to analyze the observed CO spectral line energy distributions (SLEDs). The FTS CO data were complemented with ground-based observations of the low-J CO lines. We found that the warm molecular gas traced by the mid-J CO transitions has similar physical conditions (n_H2 ~ 10^3.2 – 10^3.9 cm^-3 and T_kin ~ 300 – 800 K) in most of our galaxies. Furthermore, we found that this warm gas is likely producing the mid-IR rotational H2 emission. We could not determine the specific heating mechanism of the warm gas, however it is possibly related to the star-formation activity in these galaxies. Our modeling of the [CI] emission suggests that it is produced in cold (T_kin < 30 K) and dense (n_H2 > 10^3 cm^-3) molecular gas. Transitions of other molecules are often detected in our SPIRE/FTS spectra. The HF J=1-0 transition at 1232 GHz is detected in absorption in UGC05101 and in emission in NGC7130. In the latter, near-infrared pumping, chemical pumping, or collisional excitation with electrons are plausible excitation mechanisms likely related to the AGN of this galaxy. In some galaxies few H2O emission lines are present. Additionally, three OH+ lines at 909, 971, and 1033 GHz are identified in NGC7130.

Comments: Accepted for publication in ApJ; 20 pages, 9 figures
Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1303.3511 [astro-ph.GA]
(or arXiv:1303.3511v1 [astro-ph.GA] for this version)
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