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Register a new userCorrelations between MIR, FIR, H$alpha$, and FUV Luminosities for SWIRE galaxies
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Yi-Nan Zhu
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e present and analyze the correlations between mid-infrared (MIR), far-infrared (FIR), total-infrared (TIR), H$alpha$, and FUV luminosities for star-forming galaxies, composite galaxies and AGNs, based on a large sample of galaxies selected from the $Spitzer$ SWIRE fields. The MIR luminosities of star-forming galaxies are well correlated with their H$alpha$, TIR and FUV luminosities, and we re-scaled the MIR-derived SFR formulae according to the above correlations with differences less than 15%. We confirm the recent result by calzetti et al. (2007) that the combined observed H$alpha$ + 24$mu$m luminosities L(H$alpha$$_{rm obs}$+ 24$mu$m) possess very tight correlation with the extinction-corrected H$alpha$ luminosities L(H$alpha$$_$corr) for star-forming and even for dwarf galaxies, and show that the combined L(H$alpha$$_{rm obs}$+ 8$mu$m[dust]) are also tightly correlated with L(H$alpha$$_$corr) for the above sample galaxies. Among all the L(MIR)-L(FIR) correlations for star-forming galaxies, the L(24$mu$m) vs. L(70$mu$m) and L(8$mu$m[dust]) vs. L(160$mu$m) are the tightest and also nearly linear. The former could be related to young massive star formation, while the latter might be relevant to diffuse dust emissions heated by old stellar populations. Composite galaxies and AGNs have higher MIR-to-H$alpha$/MIR-to-FUV luminosity ratios than star-forming galaxies, nevertheless their correlations among MIR, FIR and TIR luminosities are completely following those of star-forming galaxies.
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We explore the correlation between morphological types and mid-infrared (MIR) properties of an optically flux-limited sample of 154 galaxies from the Forth Data Release (DR4) of Sloan Digital Sky Survey (SDSS), cross-correlated with Spitzer SWIRE (Spitzer Wide-Area InfraRed Extragalactic Survey) fields of ELAIS-N1, ELAIS-N2 and Lockman Hole. Aperture photometry is performed on the SDSS and Spitzer images to obtain optical and MIR properties. The morphological classifications are given based on both visual inspection and bulge-disk decomposition on SDSS g- and r-band images. The average bulge-to-total ratio (B/T) is a smooth function over different morphological types. Both the 8um(dust) and 24um(dust) luminosities and their relative luminosity ratios to 3.6um (MIR dust-to-star ratios) present obvious correlations with both the Hubble T-type and B/T. The early-type galaxies notably differ from the late-types in the MIR properties, especially in the MIR dust-to-star ratios. It is suggested that the MIR dust-to-star ratio is an effective way to separate the early-type galaxies from the late-type ones. Based on the tight correlation between the stellar mass and the 3.6um luminosity, we have derived a formula to calculate the stellar mass from the latter. We have also investigated the MIR properties of both edge-on galaxies and barred galaxies in our sample. Since they present similar MIR properties to the other sample galaxies, they do not influence the MIR properties obtained for the entire sample.
The recent finding that the IGIMF (integrated galaxial initial stellar mass function) composed of all newly formed stars in all young star clusters has, in dependence of the SFR, a steeper slope in the high mass regime than the underlying canonical IMF of each star cluster offers new insights into the galactic star formation process: The classical linear relation between the SFR and the produced H$alpha$ luminosity is broken and SFRs are always underestimated. Our new relation is likely to lead to a revision of the cosmological SFH.
We discuss optical associations, spectral energy distributions and photometric redshifts for SWIRE sources in the ELAIS-N1 area and the Lockman Validation Field. The band-merged IRAC (3.6, 4.5, 5.8 and 8.0 mu) and MIPS (24, 70, 160 mu) data have been associated with optical UgriZ data from the INT Wide Field Survey in ELAIS-N1, and with our own optical Ugri data in Lockman-VF. The spectral energy distributions of selected ELAIS sources in N1 detected by SWIRE, most with spectroscopic redshifts, are modelled in terms of a simple set of galaxy and quasar templates in the optical and near infrared, and with a set of dust emission templates (cirrus, M82 starburst, Arp 220 starburst, and AGN dust torus) in the mid infrared. The optical data, together with the IRAC 3.6 and 4.5 mu data, have been used to determine photometric redshifts. For galaxies with known spectroscopic redshifts there is a notable improvement in the photometric redshift when the IRAC data are used, with a reduction in the rms scatter from 10% in (1+z) to 7%. The photometric redshifts are used to derive the 3.6 and 24 mu redshift distribution and to compare this with the predictions of models. For those sources with a clear mid infrared excess, relative to the galaxy starlight model used for the optical and near infrared, the mid and far infrared data are modelled in terms of the same dust emission templates. The proportions found of each template type are: cirrus 31%, M82 29%, Arp 220 10%, AGN dust tori 29%. The distribution of the different infrared sed types in the L_{ir}/L_{opt} versus L_{ir} plane, where L_{ir} and L_{opt} are the infrared and optical bolometric luminosities, is discussed.
Using a sample of dwarf irregular galaxies selected from the ALFALFA blind HI-survey and observed using the VIMOS IFU, we investigate the relationship between H$alpha$ emission and Balmer optical depth ($tau_{text{b}}$). We find a positive correlation between H$alpha$ luminosity surface density and Balmer optical depth in 8 of 11 at $geq$ 0.8$sigma$ significance (6 of 11 at $geq$ 1.0$sigma$) galaxies. Our spaxels have physical scales ranging from 30 to 80 pc, demonstrating that the correlation between these two variables continues to hold down to spatial scales as low as 30 pc. Using the Spearmans rank correlation coefficient to test for correlation between $Sigma_{text{H}alpha}$ and $tau_{text{b}}$ in all the galaxies combined, we find $rho = 0.39$, indicating a positive correlation at 4$sigma$ significance. Our low stellar-mass galaxy results are in agreement with observations of emission line regions in larger spiral galaxies, indicating that this relationship is independent of the size of the galaxy hosting the emission line region. The positive correlation between H$alpha$ luminosity and Balmer optical depth within spaxels is consistent with the hypothesis that young star-forming regions are surrounded by dusty birth-clouds.
This work explores from a statistical point of view the rest-frame Far-ultraviolet (FUV) to Far-infrared (FIR) emission of a population of Lyman break galaxies (LBGs) at $zsim3$ that cannot be individually detected from current FIR observations. We perform a stacking analysis over a sample of $sim$17000 LBGs at redshift $2.5<z<3.5$ in the COSMOS field. The sample is binned as a function of UV luminosity ($L_{mathrm{FUV}}$), UV continuum slope ($beta_{mathrm{UV}}$), and stellar mass (M$_{*}$), and then, stacked at optical ($BVriz$ bands), near-infrared ($YJHKs$ bands), IRAC (3.6, 4.5, 5.6 and 8.0 $mu$m), MIPS (24$mu$m), PACS (100 and 160~$mu$m), SPIRE (250, 350, and 500~$mu$m), and AzTEC (1.1mm) observations. We obtain thirty rest-frame FUV-to-FIR spectral energy distribution (SEDs) of LBGs at $zsim3$, and analyse them with CIGALE SED-fitting analysis code. We are able to derive fully consistent physical parameters (M$_{*}$, $beta_{mathrm{UV}}$, $L_{mathrm{FUV}}$, $L_{mathrm{IR}}$, A$_{FUV}$, SFR, and slope of the dust attenuation law), and build a semi-empirical library of thirty rest-frame FUV-to-FIR stacked LBG SEDs as a function of $L_{mathrm{FUV}}$, $beta_{mathrm{UV}}$, and M$_{*}$. We used the so-called IR-excess ($IRX equiv L_{mathrm{IR}} / L_{mathrm{FUV}}$) to investigate the dust attenuation as a function of $beta_{mathrm{UV}}$ and M$_{*}$. Additionally, the SED-fitting analysis results provide a diversity of dust attenuation curve along the LBG sample, and their slope are well correlated with M$_{*}$. Stepper dust attenuations curves than Calzettis are favoured in low stellar mass LBGs ($log(M_{*} [M_{odot}]) < 10.25$), while grayer ones are favoured in high stellar mass LBGs ($log(M_{*} [M_{odot}]) > 10.25$).
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