Abstract
We investigate the connection between star formation and molecular gas properties in galaxy mergers at low redshift (z ≤ 0.06). The study we present is based on IRAM 30-m CO(1–0) ...observations of 11 galaxies with a close companion selected from the Sloan Digital Sky Survey (SDSS). The pairs have mass ratios ≤4, projected separations rp ≤ 30 kpc and velocity separations ΔV ≤ 300 km s−1, and have been selected to exhibit enhanced specific star formation rates (sSFRs). We calculate molecular gas (H2) masses, assigning to each galaxy a physically motivated conversion factor αCO, and we derive molecular gas fractions and depletion times. We compare these quantities with those of isolated galaxies from the extended CO Legacy Data base for the GALEX Arecibo SDSS Survey sample (xCOLDGASS; Saintonge et al.) with gas quantities computed in an identical way. Ours is the first study which directly compares the gas properties of galaxy pairs and those of a control sample of normal galaxies with rigorous control procedures and for which SFR and H2 masses have been estimated using the same method. We find that the galaxy pairs have shorter depletion times and an average molecular gas fraction enhancement of 0.4 dex compared to the mass matched control sample drawn from xCOLDGASS. However, the gas masses (and fractions) in galaxy pairs and their depletion times are consistent with those of non-mergers whose SFRs are similarly elevated. We conclude that both external interactions and internal processes may lead to molecular gas enhancement and decreased depletion times.
We present and maps of six nearby star-forming galaxies, NGC 253, NGC 1068, IC 342, M82, M83, and NGC 6946, obtained with the James Clerk Maxwell Telescope as part of the MALATANG survey. All ...galaxies were mapped in the central 2′ × 2′ region at 14″ (FWHM) resolution (corresponding to linear scales of ∼0.2-1.0 kpc). The LIR-L′dense relation, where the dense gas is traced by the and the emission, measured in our sample of spatially resolved galaxies is found to follow the linear correlation established globally in galaxies within the scatter. We find that the luminosity ratio, LIR/L′dense, shows systematic variations with LIR within individual spatially resolved galaxies, whereas the galaxy-integrated ratios vary little. A rising trend is also found between LIR/L′dense ratio and the warm-dust temperature gauged by the 70 m/100 m flux ratio. We find that the luminosity ratios of IR/HCN (4-3) and IR/HCO+ (4-3), which can be taken as a proxy for the star formation efficiency (SFE) in the dense molecular gas (SFEdense), appear to be nearly independent of the dense gas fraction (fdense) for our sample of galaxies. The SFE of the total molecular gas (SFEmol) is found to increase substantially with fdense when combining our data with those on local (ultra)luminous infrared galaxies and high-z quasars. The mean line ratio measured for the six targeted galaxies is 0.9 0.6. No significant correlation is found for the ratio with the star formation rate as traced by LIR, nor with the warm-dust temperature, for the different populations of galaxies.
ABSTRACT
We present a detailed study of a high-redshift iron low-ionization broad absorption line (FeLoBAL) quasar (SDSS1214 at $z$ = 1.046), including new interferometric 12CO J = 2–1 observations, ...optical through far-infrared photometry, and mid-infrared spectroscopy. The CO line is well fit by a single Gaussian centred 40 km s−1 away from the systemic velocity and implies a total molecular gas mass of $M_{\rm gas} = 7.3 \times 10^{10}\, {\rm M}_\odot$. The infrared spectral energy distribution requires three components: an active galactic nucleus (AGN) torus, an AGN polar dust component, and a starburst. The starburst dominates the infrared emission with a luminosity of log$(L_{\rm SB}{\rm L}_\odot ) = 12.91^{+0.02}_{-0.02}$, implying a star formation rate of about 2000 M⊙yr−1, the highest known among FeLoBAL quasars. The AGN torus and polar dust components are less luminous, at log$(L_{\rm AGN}{\rm L}_\odot ) = 12.36^{+0.14}_{-0.15}$ and log$(L_{\rm dust}{\rm L}_\odot ) = 11.75^{+0.26}_{-0.46}$, respectively. If all of the molecular gas is used to fuel the ongoing star formation, then the lower limit on the subsequent duration of the starburst is 40 Myr. We do not find conclusive evidence that the AGN is affecting the CO gas reservoir. The properties of SDSS1214 are consistent with it representing the endpoint of an obscured starburst transitioning through a LoBAL phase to that of a classical quasar.
Abstract
We present
and
maps of six nearby star-forming galaxies, NGC 253, NGC 1068, IC 342, M82, M83, and NGC 6946, obtained with the James Clerk Maxwell Telescope as part of the MALATANG survey. ...All galaxies were mapped in the central 2′ × 2′ region at 14″ (FWHM) resolution (corresponding to linear scales of ∼0.2–1.0 kpc). The
L
IR
–
L
′
dense
relation, where the dense gas is traced by the
and the
emission, measured in our sample of spatially resolved galaxies is found to follow the linear correlation established globally in galaxies within the scatter. We find that the luminosity ratio,
L
IR
/
L
′
dense
, shows systematic variations with
L
IR
within individual spatially resolved galaxies, whereas the galaxy-integrated ratios vary little. A rising trend is also found between
L
IR
/
L
′
dense
ratio and the warm-dust temperature gauged by the 70
μ
m/100
μ
m flux ratio. We find that the luminosity ratios of IR/HCN (4–3) and IR/HCO
+
(4–3), which can be taken as a proxy for the star formation efficiency (SFE) in the dense molecular gas (SFE
dense
), appear to be nearly independent of the dense gas fraction (
f
dense
) for our sample of galaxies. The SFE of the total molecular gas (SFE
mol
) is found to increase substantially with
f
dense
when combining our data with those on local (ultra)luminous infrared galaxies and high-
z
quasars. The mean
line ratio measured for the six targeted galaxies is 0.9 ± 0.6. No significant correlation is found for the
ratio with the star formation rate as traced by
L
IR
, nor with the warm-dust temperature, for the different populations of galaxies.
It is thought that a class of broad absorption line (BAL) QSOs, characterized by Fe absorption features in their UV spectra (called 'FeLoBALs'), could mark a transition stage between the end of an ...obscured starburst event and a youthful QSO beginning to shed its dust cocoon, where Fe has been injected into the interstellar medium by the starburst. To test this hypothesis, we have undertaken deep Submillimetre Common-User Bolometer Array 2 (SCUBA-2) 850 mu m observations of a sample of 17 FeLoBAL QSOs with 0.89 less than or equal to z less than or equal to 2.78 and -23.31 less than or equal to MB less than or equal to -28.50 to directly detect an excess in the thermal emission of the dust which would probe enhanced star formation activity. We find that FeLoBALs are not luminous sources in the sub-mm, none of them are individually detected at 850 mu m, nor as a population through stacking (Fs = 1.14 plus or minus 0.58 mJy). Statistical and survival analyses reveal that FeLoBALs have sub-mm properties consistent with BAL and non-BAL QSOs with matched redshifts and magnitudes. An Spectral Energy Distribution fitting analysis shows that the far-infrared emission is dominated by active galactic nuclei activity, and a starburst component is required only in 6/17 sources of our sample; moreover the integrated total luminosity of 16/17 sources is L greater than or equal to 10 super( 12) L..., high enough to classify FeLoBALs as infrared luminous. In conclusion, we do not find any evidence in support of FeLoBAL QSOs being a transition population between an ultraluminous infrared galaxy (ULIRG) and an unobscured QSO; in particular, FeLoBALs are not characterized by a cold starburst which would support this hypothesis. (ProQuest: ... denotes formulae/symbols omitted.)
We present a detailed study of a high-redshift iron low-ionization broad absorption line (FeLoBAL) quasar (SDSS1214 at \(z = 1.046\)), including new interferometric \(^{12}\)CO \(J\)=2-1 ...observations, optical through far-infrared photometry, and mid-infrared spectroscopy. The CO line is well-fit by a single Gaussian centered 40 kms\(^{-1}\) away from the systemic velocity and implies a total molecular gas mass of \(M_\textrm{gas} = 7.3 \times 10^{10} \textrm{M}_\odot\). The infrared SED requires three components: an active galactic nucleus (AGN) torus, an AGN polar dust component, and a starburst. The starburst dominates the infrared emission with a luminosity of log(\(L_\textrm{SB}\textrm{L}_\odot) = 12.91^{+0.02}_{-0.02}\), implying a star formation rate of about 2000 \(\textrm{M}_{\odot}\)yr\(^{-1}\), the highest known among FeLoBAL quasars. The AGN torus and polar dust components are less luminous, at log(\(L_\textrm{AGN}\textrm{L}_\odot) = 12.36^{+0.14}_{-0.15}\) and log(\(L_\textrm{dust}\textrm{L}_\odot) = 11.75^{+0.26}_{-0.46}\), respectively. If all of the molecular gas is used to fuel the ongoing star formation, then the lower limit on the subsequent duration of the starburst is 40 Myr. We do not find conclusive evidence that the AGN is affecting the CO gas reservoir. The properties of SDSS1214 are consistent with it representing the endpoint of an obscured starburst transitioning through a LoBAL phase to that of a classical quasar.
We investigate the connection between star formation and molecular gas properties in galaxy mergers at low redshift (z\(\leq\)0.06). The study we present is based on IRAM 30-m CO(1-0) observations of ...11 galaxies with a close companion selected from the Sloan Digital Sky Survey (SDSS). The pairs have mass ratios \(\leq\)4, projected separations r\(_{\mathrm{p}} \leq\)30 kpc and velocity separations \(\Delta\)V\(\leq\)300 km s\(^{-1}\), and have been selected to exhibit enhanced specific star formation rates (sSFR). We calculate molecular gas (H\(_{2}\)) masses, assigning to each galaxy a physically motivated conversion factor \(\alpha_{\mathrm{CO}}\), and we derive molecular gas fractions and depletion times. We compare these quantities with those of isolated galaxies from the extended CO Legacy Data base for the GALEX Arecibo SDSS Survey sample (xCOLDGASS, Saintonge et al. 2017) with gas quantities computed in an identical way. Ours is the first study which directly compares the gas properties of galaxy pairs and those of a control sample of normal galaxies with rigorous control procedures and for which SFR and H\(_{2}\) masses have been estimated using the same method. We find that the galaxy pairs have shorter depletion times and an average molecular gas fraction enhancement of 0.4 dex compared to the mass matched control sample drawn from xCOLDGASS. However, the gas masses (and fractions) in galaxy pairs and their depletion times are consistent with those of non-mergers whose SFRs are similarly elevated. We conclude that both external interactions and internal processes may lead to molecular gas enhancement and decreased depletion times.
It is thought that a class of broad absorption line (BAL) QSOs, characterised by Fe absorption features in their UV spectra (called `FeLoBALs'), could mark a transition stage between the end of an ...obscured starburst event and a youthful QSO beginning to shed its dust cocoon, where Fe has been injected into the interstellar medium by the starburst. To test this hypothesis we have undertaken deep SCUBA-2 850 \(\mu\)m observations of a sample of 17 FeLoBAL QSOs with 0.89 \(\leq\) z \(\leq\) 2.78 and -23.31 \(\leq\) M\(_{B}\) \(\leq\)-28.50 to directly detect an excess in the thermal emission of the dust which would probe enhanced star-formation activity. We find that FeLoBALs are not luminous sources in the submillimetre, none of them are individually detected at 850 \(\mu\)m, nor as a population through stacking (\(F_{s}=1.14\pm0.58\) mJy). Statistical and survival analyses reveal that FeLoBALs have sub-mm properties consistent with BAL and non-BAL QSOs with matched redshifts and magnitudes. An SED fitting analysis shows that the FIR emission is dominated by AGN activity, and a starburst component is required only in 6/17 sources of our sample; moreover the integrated total luminosity of 16/17 sources is L\(\geq\)10\(^{12}\)L\(_{\odot}\), high enough to classify FeLoBALs as infrared luminous. In conclusion, we do not find any evidence in support of FeLoBAL QSOs being a transition population between a ULIRG and an unobscured QSO; in particular, FeLoBALs are not characterized by a cold starburst which would support this hypothesis.
We present HCN J=4-3 and HCO^+ J=4-3 maps of six nearby star-forming galaxies, NGC 253, NGC 1068, IC 342, M82, M83, and NGC 6946, obtained with the James Clerk Maxwell Telescope as part of the ...MALATANG survey. All galaxies were mapped in the central 2 arcmin \(\times\) 2 arcmin region at 14 arcsec (FWHM) resolution (corresponding to linear scales of ~ 0.2-1.0 kpc). The L_IR-L'_dense relation, where the dense gas is traced by the HCN J=4-3 and the HCO^+ J=4-3 emission, measured in our sample of spatially-resolved galaxies is found to follow the linear correlation established globally in galaxies within the scatter. We find that the luminosity ratio, L_IR/L'_dense, shows systematic variations with L_IR within individual spatially resolved galaxies, whereas the galaxy-integrated ratios vary little. A rising trend is also found between L_IR/L'_dense ratio and the warm-dust temperature gauged by the 70 \mu m/100 \mu m flux ratio. We find the luminosity ratios of IR/HCN(4-3) and IR/HCO^+(4-3), which can be taken as a proxy for the efficiency of star formation in the dense molecular gas (SFE_dense), appears to be nearly independent of the dense-gas fraction (f_dense) for our sample of galaxies. The SFE of the total molecular gas (SFE_mol) is found to increase substantially with f_dense when combining our data with that on local (ultra)luminous infrared galaxies and high-z quasars. The mean L'_HCN(4-3)/L'_HCO^+(4-3) line ratio measured for the six targeted galaxies is 0.9+/-0.6. No significant correlation is found for the L'_HCN(4-3)/L'_HCO^+(4-3) ratio with the SFR as traced by L_IR, nor with the warm-dust temperature, for the different populations of galaxies.
JINGLE is a new JCMT legacy survey designed to systematically study the cold interstellar medium of galaxies in the local Universe. As part of the survey we perform 850um continuum measurements with ...SCUBA-2 for a representative sample of 193 Herschel-selected galaxies with M*>10^9Msun, as well as integrated CO(2-1) line fluxes with RxA3m for a subset of 90 of these galaxies. The sample is selected from fields covered by the Herschel-ATLAS survey that are also targeted by the MaNGA optical integral-field spectroscopic survey. The new JCMT observations combined with the multi-wavelength ancillary data will allow for the robust characterization of the properties of dust in the nearby Universe, and the benchmarking of scaling relations between dust, gas, and global galaxy properties. In this paper we give an overview of the survey objectives and details about the sample selection and JCMT observations, present a consistent 30 band UV-to-FIR photometric catalog with derived properties, and introduce the JINGLE Main Data Release (MDR). Science highlights include the non-linearity of the relation between 850um luminosity and CO line luminosity, and the serendipitous discovery of candidate z>6 galaxies.
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