In this article, the authors present the first results of a survey of the [C II]157.7 {$μ$}m emission line in 241 luminous infrared galaxies (LIRGs) comprising the Great Observatories All-sky LIRG Survey (GOALS) sample, obtained with the PACS instrument on board the Herschel Space Observatory.
Abstract:
We present the first results of a survey of the [C II]157.7 {$μ$}m emission line in 241 luminous infrared galaxies (LIRGs) comprising the Great Observatories All-sky LIRG Survey (GOALS) sample, obtained with the PACS instrument on board the Herschel Space Observatory. The [C II] luminosities, L $_{[C II]}$, of the LIRGs in GOALS range from ~{}10$^{7}$ to 2 { imes} 10$^{9}$ L $_{⊙}$. We find that LIRGs show a tight correlation of [C II]/FIR with far-IR (FIR) flux density ratios, with a strong negative trend spanning from ~{}10$^{-2}$ to 10$^{-4}$, as the average temperature of dust increases. We find correlations between the [C II]/FIR ratio and the strength of the 9.7 {$μ$}m silicate absorption feature as well as with the luminosity surface density of the mid-IR emitting region ({$Sigma$}$_{MIR}$), suggesting that warmer, more compact starbursts have substantially smaller [C II]/FIR ratios. Pure star-forming LIRGs have a mean [C II]/FIR ~{} 4 { imes} 10$^{-3}$, while galaxies with low polycyclic aromatic hydrocarbon (PAH) equivalent widths (EWs), indicative of the presence of active galactic nuclei (AGNs), span the full range in [C II]/FIR. However, we show that even when only pure star-forming galaxies are considered, the [C II]/FIR ratio still drops by an order of magnitude, from 10$^{-2}$ to 10$^{-3}$, with {$Sigma$}$_{MIR}$ and {$Sigma$}$_{IR}$, implying that the [C II]157.7 {$μ$}m luminosity is not a good indicator of the star formation rate (SFR) for most local LIRGs, for it does not scale linearly with the warm dust emission most likely associated to the youngest stars. Moreover, even in LIRGs in which we detect an AGN in the mid-IR, the majority (2/3) of galaxies show [C II]/FIR {gt}= 10$^{-3}$ typical of high 6.2 {$μ$}m PAH EW sources, suggesting that most AGNs do not contribute significantly to the FIR emission. We provide an empirical relation between the [C II]/FIR and the specific SFR for star-forming LIRGs. Finally, we present predictions for the starburst size based on the observed [C II] and FIR luminosities which should be useful for comparing with results from future surveys of high-redshift galaxies with ALMA and CCAT.
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TL;DR: In this paper, the authors used the high-resolution near-infrared data to recover nuclear structure that is obscured by dust at optical wavelengths and measure the evolution in this structure along the merger sequence.
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TL;DR: In this paper, the authors used high-resolution near-infrared data to recover nuclear structure that is obscured by dust at optical wavelengths and measure the evolution in this structure along the merger sequence.
TL;DR: In this paper, the authors explore the relationship between the polycyclic aromatic hydrocarbon (PAH) feature strengths, mid-infrared continuum luminosities, far infrared spectral slopes, optical spectroscopic classifications and silicate optical depths in a sample of 107 ULIRGs observed with the Infrared Spectrograph on the Spitzer Space Telescope.
The authors present the first results of a survey of the [ C ii ] 157. The authors find that LIRGs show a tight correlation of [ C ii ] /FIR with far-IR ( FIR ) flux density ratios, with a strong negative trend spanning from ∼10−2 to 10−4, as the average temperature of dust increases. However, the authors show that even when only pure star-forming galaxies are considered, the [ C ii ] /FIR ratio still drops by an order of magnitude, from 10−2 to 10−3, with ΣMIR and ΣIR, implying that the [ C ii ] 157. Moreover, even in LIRGs in which the authors detect an AGN in the mid-IR, the majority ( 2/3 ) of galaxies show [ C ii ] /FIR 10−3 typical of high 6. 2 μm PAH EW sources, suggesting that most AGNs do not contribute significantly to the FIR emission. The authors provide an empirical relation between the [ C ii ] /FIR and the specific SFR for star-forming LIRGs. Finally, the authors present predictions for the starburst size based on the observed [ C ii ] and FIR luminosities which should be useful for comparing with results from future surveys of high-redshift galaxies with ALMA and CCAT. 7 μm silicate absorption feature as well as with the luminosity surface density of the mid-IR emitting region ( ΣMIR ), suggesting that warmer, more compact starbursts have substantially smaller [ C ii ] /FIR ratios.
Q2. What is the important source of photo-electrons?
In particular, polycyclic aromatic hydrocarbons (PAHs) are thought to be an important source of photo-electrons (Helou et al. 2001) that contribute, through kinetic energy transfer, to the heating of the neutral gas which subsequently cools down via collision with C+ atoms and other elements in photo-dissociation regions (PDRs; Tielens & Hollenbach 1985; Wolfire et al. 1995).
Q3. What is the net effect of the emission of dust particles?
The net effect is the decreasing of the efficiency in the transformation of incident UV radiation into gas heating without an accompanied reduction of the dust emission (Wolfire et al.
Q4. What is the trend for LIRGs with deeper silicate strengths?
There is a clear trend for LIRGs with deeper 9.7 μm silicate strengths (S9.7 μm), higher mid-IR luminosity surface densities (ΣMIR), smaller fractions of extended emission (FEE13.2 μm) and higher SSFRs to display lower [C ii]/FIR ratios.
Q5. How many spectral elements are in each pixel?
The number of spectral elements in each pixel is 16, which are rearranged together via an image slicer over two 16 × 25 Ge:Ga detector arrays (blue and red cameras).
Q6. What is the FIR ratio for the GOALS sample?
Figure 2 (upper panel) shows the [C ii]157.7 μm/FIR ratio for the GOALS sample as a function of the FIR PACS Sν 63 μm/ Sν 158 μm continuum flux density ratio.
Q7. Why is the [C ii] line less efficient?
It has also been suggested that in sources where G0/nH is high ( 102 cm3) the [C ii] line is a less efficient coolant of the ISM because of the following reason.