We present the results of a Herschel-PACS study of a sample of 97 low-ionization nuclear emission-line regions (LINERs) at redshift z 0.3 selected from the zCOSMOS survey. Of these sources, 34 are detected in at least one PACS band, enabling reliable estimates of the far-infrared L FIR luminosities, and a comparison to the FIR luminosities of local LINERs. Many of our PACS-detected LINERs are also UV sources detected by GALEX. Assuming that the FIR is produced in young dusty star-forming regions, the typical star formation rates (SFRs) for the host galaxies in our sample are 10 M yr -1, 1-2 orders of magnitude larger than in many local LINERs. Given stellar masses inferred from optical/NIR photometry of the (unobscured) evolved stellar populations, we find that the entire sample lies close to the star-forming "main sequence" for galaxies at redshift 0.3. For young star-forming regions, the Hα- and UV-based estimates of the SFRs are much smaller than the FIR-based estimates, by factors 30, even assuming that all of the Hα emission is produced by O-star ionization rather than by the active galactic nuclei (AGNs). These discrepancies may be due to large (and uncertain) extinctions toward the young stellar systems. Alternatively, the Hα and UV emissions could be tracing residual star formation in an older, less obscured population with decaying star formation. We also compare L SF and L(AGN) in local LINERs and in our sample. Finally, we comment on the problematic use of several line diagnostic diagrams in cases with an estimated obscuration similar to that in the sample under study.
Star formation in liner host galaxies at z ∼ 0.3
Tommasin, Silvia;
2012-01-01
Abstract
We present the results of a Herschel-PACS study of a sample of 97 low-ionization nuclear emission-line regions (LINERs) at redshift z 0.3 selected from the zCOSMOS survey. Of these sources, 34 are detected in at least one PACS band, enabling reliable estimates of the far-infrared L FIR luminosities, and a comparison to the FIR luminosities of local LINERs. Many of our PACS-detected LINERs are also UV sources detected by GALEX. Assuming that the FIR is produced in young dusty star-forming regions, the typical star formation rates (SFRs) for the host galaxies in our sample are 10 M yr -1, 1-2 orders of magnitude larger than in many local LINERs. Given stellar masses inferred from optical/NIR photometry of the (unobscured) evolved stellar populations, we find that the entire sample lies close to the star-forming "main sequence" for galaxies at redshift 0.3. For young star-forming regions, the Hα- and UV-based estimates of the SFRs are much smaller than the FIR-based estimates, by factors 30, even assuming that all of the Hα emission is produced by O-star ionization rather than by the active galactic nuclei (AGNs). These discrepancies may be due to large (and uncertain) extinctions toward the young stellar systems. Alternatively, the Hα and UV emissions could be tracing residual star formation in an older, less obscured population with decaying star formation. We also compare L SF and L(AGN) in local LINERs and in our sample. Finally, we comment on the problematic use of several line diagnostic diagrams in cases with an estimated obscuration similar to that in the sample under study.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
