Wednesday 1st Aug 2012


Title: The Mid-IR Contribution Of Dust Enshrouded Stars In Six Nearby Galaxies

Authors: J. R. Gerke, C. S. Kochanek

We measure the integrated contributions of dusty AGB stars and other luminous red sources to the mid-IR luminosities of 6 galaxies (M81, NGC 2403, NGC 300, M33 and the Magellanic Clouds). We find the dusty AGB stars contribute from 0.6% (M81) to 5.6% (SMC) of the 3.6 micron flux and 1.0% (M81) to 10.1% (SMC) of the 4.5 micron flux. We find a trend of decreasing AGB contribution with increasing galaxy metallicity, luminosity and mass and decreasing SSRF. However, these galaxy properties are strongly correlated in our sample and the most likely explanation of the trend is galaxy metallicity. The bright, red sources represent a smaller fraction of the luminosity, ~1.2% at 3.6 microns, however their dust is likely cooler and their contributions are likely larger at longer wavelengths. Excluding the SMC, the contribution from these sources correlates with the specific star formation rate as we would expect for massive stars. In total, after correcting for dust emission at other wavelengths, the dust around AGB stars radiates 0.1-0.8% of the bolometric luminosities of the galaxies. Thus, hot dust emission from AGB and other luminous dusty stars represent a small fraction of the total luminosities of the galaxies but a significant fraction of their mid-IR emissions.


Title: GOODS-Herschel: Ultra-deep XMM-Newton observations reveal AGN/star-formation connection

Authors: E. Rovilos, A. Comastri, R. Gilli, I. Georgantopoulos, P. Ranalli, C. Vignali, E. Lusso, N. Cappelluti, G. Zamorani, D. Elbaz, M. Dickinson, H. S. Hwang, V. Charmandaris, R. J. Ivison, A. Merloni, E. Daddi, F. J. Carrera, W. N. Brandt, J. R. Mullaney, D. Scott, D. M. Alexander, A. Del Moro, G. Morrison, E. J. Murphy, B. Altieri, H. Aussel, H. Dannerbauer, J. Kartaltepe, R. Leiton, G. Magdis, B. Magnelli, P. Popesso, I. Valtchanov

Models of galaxy evolution assume some connection between the AGN and star formation activity in galaxies. We use the multi-wavelength information of the CDFS to assess this issue. We select the AGNs from the 3Ms XMM-Newton survey and measure the star-formation rates of their hosts using data that probe rest-frame wavelengths longward of 20 um. Star-formation rates are obtained from spectral energy distribution fits, identifying and subtracting an AGN component. We divide the star-formation rates by the stellar masses of the hosts to derive specific star-formation rates (sSFR) and find evidence for a positive correlation between the AGN activity (proxied by the X-ray luminosity) and the sSFR for the most active systems with X-ray luminosities exceeding Lx=10^43 erg/s and redshifts z~1. We do not find evidence for such a correlation for lower luminosity systems or those at lower redshifts. We do not find any correlation between the SFR (or the sSFR) and the X-ray absorption derived from high-quality XMM-Newton spectra either, showing that the absorption is likely to be linked to the nuclear region rather than the host, while the star-formation is not nuclear. Comparing the sSFR of the hosts to the characteristic sSFR of star-forming galaxies at the same redshift we find that the AGNs reside mostly in main-sequence and starburst hosts, reflecting the AGN – sSFR connection. Limiting our analysis to the highest X-ray luminosity AGNs (X-ray QSOs with Lx>10^44 erg/s), we find that the highest-redshift QSOs (with z>2) reside predominantly in starburst hosts, with an average sSFR more than double that of the "main sequence", and we find a few cases of QSOs at z~1.5 with specific star-formation rates compatible with the main-sequence, or even in the "quiescent" region. (abridged)

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