The star formation history of redshift z ~ 2 galaxies： the role of the infrared prior

• Published in: Research in astronomy and astrophysics Vol. 14; no. 1; pp. 15 - 34
• Main Authors: Fan, Lu-Lu, Lapi, Andrea, Bressan, Alessandro, Nonino, Mario, De Zotti, Gianfranco, Danese, Luigi
• Format: Journal Article
• Language: English
• Published: 2014
• Subjects: Construction; Estimates; Galaxies; Luminosity; Red shift; SFR; Stellar mass; 历史; 恒星形成率; 拟合技术; 星系红移; 物理参数; 红外光度; 红外线
• ISSN: 1674-4527; 2397-6209
• DOI: 10.1088/1674-4527/14/1/002

We build a sample of 298 spectroscopically-confirmed galaxies at redshift z - 2, selected in the z850-band from the GOODS-MUSIC catalog. By utilizing the rest frame 8 p.m luminosity as a proxy of the star formation rate （SFR）, we check the accuracy of the standard SED-fitting technique, finding it is not accurate enough to provide reliable estimates of the physical parameters of galaxies. We then develop a new SED-fitting method that includes the IR luminosity as a prior and a generalized Calzetti law with a variable Rv. Then we exploit the new method to re-analyze our galaxy sample, and to robustly determine SFRs, stellar masses and ages. We find that there is a general trend of increasing attenuation with the SFR. Moreover, we find that the SFRs range between a few to 103 M~ yr-1, the masses from 109 to 4 ~ 1011 Mo, and the ages from a few tens of Myr to more than 1 Gyr. We discuss how individual age measurements of highly attenuated objects indicate that dust must have formed within a few tens of Myr and already been copious at 〈 100 Myr. In addition, we find that low luminosity galaxies harbor, on average, significantly older stellar populations and are also less massive than brighter ones; we discuss how these findings and the well known ＇downsizing＇ scenario are consistent in a framework where less massive galaxies form first, but their star formation lasts longer. Finally, we find that the near-IR attenuation is not scarce for luminous objects, contrary to what is customarily assumed; we discuss how this affects the interpretation of the observed M,/L ratios.