1,024 research outputs found

    Insights on star formation histories and physical properties of 1.2≤z≲41.2 \leq z \lesssim 4 Herschel-detected galaxies

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    We test the impact of using variable star forming histories (SFHs) and the use of the IR luminosity (LIR) as a constrain on the physical parameters of high redshift dusty star-forming galaxies. We explore in particular the stellar properties of galaxies in relation with their location on the SFR-M* diagram. We perform SED fitting of the UV-NIR and FIR emissions of a large sample of GOODS-Herschel galaxies, for which rich multi-wavelength observations are available. We test different SFHs and imposing energy conservation in the SED fitting process, to face issues like the age-extinction degeneracy and produce SEDs consistent with observations. Our models work well for the majority of the sample, with the notable exception of the high LIR end, for which we have indications that our simple energy conservation approach cannot hold true. We find trends in the SFHs fitting our sources depending on stellar mass M* and z. Trends also emerge in the characteristic timescales of the SED models depending on the location on the SFR-M* diagram. We show that whilst using the same available observational data, we can produce galaxies less star-forming than usually inferred, if we allow declining SFHs, while properly reproducing their observables. These sources can be post-starbursts undergoing quenching, and their SFRs are potentially overestimated if inferred from their LIR. Fitting without the IR constrain leads to a strong preference for declining SFHs, while its inclusion increases the preference of rising SFHs, more so at high z, in tentative agreement with the cosmic star formation history. Keeping in mind that the sample is biased towards high LIR, the evolution shaped by our model appears as both bursty (initially) and steady-lasting (later on). The global SFH of the sample follows the cosmic SFH with a small scatter, and is compatible with the "downsizing" scenario of galaxy evolution.Comment: 28 pages, 26 figures, one appendix, Accepted for publication in Astronomy & Astrophysic

    Star formation rates of distant luminous infrared galaxies derived from Halpha and IR luminosities

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    We present a study of the star formation rate (SFR) for a sample of 16 distant galaxies detected by ISOCAM at 15um in the CFRS0300+00 and CFRS1400+52 fields. Their high quality and intermediate resolution VLT/FORS spectra have allowed a proper correction of the Balmer emission lines from the underlying absorption. Extinction estimates using the Hbeta/Hgamma and the Halpha/Hbeta Balmer decrement are in excellent agreement, providing a robust measurement of the instantaneous SFR based on the extinction-corrected Halpha luminosity. Star formation has also been estimated exploiting the correlations between IR luminosity and those at MIR and radio wavelengths. Our study shows that the relationship between the two SFR estimates follow two distinct regimes: (1) for galaxies with SFRIR below ~ 100Msolar/yr, the SFR deduced from Halpha measurements is a good approximation of the global SFR and (2) for galaxies near of ULIRGs regime, corrected Halpha SFR understimated the SFR by a factor of 1.5 to 2. Our analyses suggest that heavily extincted regions completely hidden in optical bands (such as those found in Arp 220) contribute to less than 20% of the global budget of star formation history up to z=1.Comment: (1) GEPI, Obs. Meudon, France ;(2) CEA-Saclay, France ;(3) ESO, Gemany ;(4) IAC, Spain. To appear in A&

    Observational evidence for the presence of PAHs in distant Luminous Infrared Galaxies using ISO and Spitzer

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    We present ISOCAM 15 micron and MIPS 24 micron photometry of a sample of 16 distant Luminous Infrared Galaxies (LIRGs) characterized by a median luminosity L(IR) 2x10^11 Lsol and redshift z = 0.7 (distributed from z = 0.1 to 1.2). While some sources display 24/15 micron flux ratios also consistent with a featureless continuum dominating their mid-infrared (MIR) spectral energy distributions (SEDs), the presence of prominent emission features such as the Polycyclic Aromatic Hydrocarbons is clearly required to explain the observed colors for more than half of the sample. As a result, a general good agreement is observed between the data and predictions from the local starburst-dominated SEDs that have been used so far to constrain IR galaxy evolution. This is consistent with the star-forming nature of LIRGs derived from previous works, even though our approach cannot rule out the dominance of an AGN in some cases. Our study also supports the possibility of tracing the total IR luminosity of distant galaxies (up to z ~ 1) from their MIR emission.Comment: 4 pages, 3 figures, Astronomy & Astrophysics Letters (in press
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