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SHINING, A Survey of Far Infrared Lines in Nearby Galaxies. I: Survey Description, Observational Trends, and Line Diagnostics

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 نشر من قبل Rodrigo Herrera-Camus
 تاريخ النشر 2018
  مجال البحث فيزياء
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We use the Herschel/PACS spectrometer to study the global and spatially resolved far-infrared (FIR) fine-structure line emission in a sample of 52 galaxies that constitute the SHINING survey. These galaxies include star-forming, active-galactic nuclei (AGN), and luminous infrared galaxies (LIRGs). We find an increasing number of galaxies (and kiloparsec size regions within galaxies) with low line-to-FIR continuum ratios as a function of increasing FIR luminosity ($L_{mathrm{FIR}}$), dust infrared color, $L_{mathrm{FIR}}$ to molecular gas mass ratio ($L_{mathrm{FIR}}/M_{mathrm{mol}}$), and FIR surface brightness ($Sigma_{mathrm{FIR}}$). The correlations between the [CII]/FIR or [OI]/FIR ratios with $Sigma_{mathrm{FIR}}$ are remarkably tight ($sim0.3$ dex scatter over almost four orders of magnitude in $Sigma_{mathrm{FIR}}$). We observe that galaxies with $L_{mathrm{FIR}}/M_{mathrm{mol}} gtrsim 80,L_{odot},M_{odot}^{-1}$ and $Sigma_{mathrm{FIR}}gtrsim10^{11}$ $L_{odot}$ kpc$^{-2}$ tend to have weak fine-structure line-to-FIR continuum ratios, and that LIRGs with infrared sizes $gtrsim1$ kpc have line-to-FIR ratios comparable to those observed in typical star-forming galaxies. We analyze the physical mechanisms driving these trends in Paper II (Herrera-Camus et al. 2018). The combined analysis of the [CII], [NII], and [OIII] lines reveals that the fraction of the [CII] line emission that arises from neutral gas increases from 60% to 90% in the most active star-forming regions and that the emission originating in the ionized gas is associated with low-ionization, diffuse gas rather than with dense gas in HII regions. Finally, we report the global and spatially resolved line fluxes of the SHINING galaxies to enable the comparison and planning of future local and high-$z$ studies.



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The SHINING survey (Paper I; Herrera-Camus et al. 2018) offers a great opportunity to study the properties of the ionized and neutral media of galaxies from prototypical starbursts and active galactic nuclei (AGN) to heavily obscured objects. Based o n Herschel/PACS observations of the main far-infrared (FIR) fine-structure lines, in this paper we analyze the physical mechanisms behind the observed line deficits in galaxies, the apparent offset of luminous infrared galaxies (LIRGs) from the mass-metallicity relation, and the scaling relations between [CII] 158 $mu$m line emission and star formation rate (SFR). Based on a toy model and the Cloudy code, we conclude that the increase in the ionization parameter with FIR surface brightness can explain the observed decrease in the line-to-FIR continuum ratio of galaxies. In the case of the [CII] line, the increase in the ionization parameter is accompanied by a reduction in the photoelectric heating efficiency and the inability of the line to track the increase in the FUV radiation field as galaxies become more compact and luminous. In the central $sim$kiloparsec regions of AGN galaxies we observe a significant increase in the [OI] 63 $mu$m/[CII] line ratio; the AGN impact on the line-to-FIR ratios fades on global scales. Based on extinction-insensitive metallicity measurements of LIRGs we confirm that they lie below the mass-metallicity relation, but the offset is smaller than those reported in studies that use optical-based metal abundances. Finally, we present scaling relations between [CII] emission and SFR in the context of the main-sequence of star-forming galaxies.
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