A 2–3 mm high-resolution molecular line survey towards the centre of the nearby spiral galaxy NGC 6946

Eibensteiner, Cosima; Barnes, Ashley T.; Bigiel, Frank; Schinnerer, E.; Liu, Daizhong; Meier, David S.; Usero, A.; Leroy, Adam K.; Rosolowsky, Erik; Puschnig, Johannes; Lazar, Ilin; Pety, J.; Lopez, Laura A.; Emsellem, Éric; Bešlić, Ivana; Murphy, E. J.; Brok, Jakob S. den; Schruba, Andreas; Chevance, Mélanie; Glover, Simon C. O.; Gao, Yu; Grasha, Kathryn; Hassani, Hamid; Henshaw, Jonathan D.; Jiménez-Donaire, María J.; Klessen, Ralf S.; Kruijssen, J. M. Diederik; Pan, Hsi-An; Saito, Toshiki; Sormani, Mattia C.; Teng, Yu-Hsuan; Williams, Thomas G.

doi:10.1051/0004-6361/202142624

“…The temperatures inferred from the HCN/HNC thermometer in NGC 4526 are roughly a factor of 2 higher than those inferred from the HNCO transitions. Discrepancies of similar magnitude are found in other extragalactic studies (Eibensteiner et al 2022), which also conclude that HCN/HNC may not be reliable for extragalactic temperature measurements. In principle, HNCO measurement is less susceptible to systematic uncertainties as it utilizes two transitions from the same molecule.…”

Section: Hcn/hncsupporting

confidence: 65%

Down but Not Out: Properties of the Molecular Gas in the Stripped Virgo Cluster Early-type Galaxy NGC 4526

Young

¹

,

Meier

²

,

Crocker

³

et al. 2022

ApJ

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We present Atacama Large Millimeter/submillimeter Array data on the 3 mm continuum emission, CO isotopologues (12CO, 13CO, and C18O), and high-density molecular tracers (HCN, HCO+, HNC, HNCO, CS, CN, and CH3OH) in NGC 4526. These data enable a detailed study of the physical properties of the molecular gas in a longtime resident of the Virgo Cluster; comparisons to more commonly studied spiral galaxies offer intriguing hints into the processing of molecular gas in the cluster environment. Many molecular line ratios in NGC 4526, along with our inferred abundances and CO/H2 conversion factors, are similar to those found in nearby spirals. One striking exception is the very low observed 12CO/13CO(1−0) line ratio, 3.4 ± 0.3, which is unusually low for spirals though not for Virgo Cluster early-type galaxies. We carry out radiative transfer modeling of the CO isotopologues with some archival (2−1) data, and we use Bayesian analysis with Markov Chain Monte Carlo techniques to infer the physical properties of the CO-emitting gas. We find surprisingly low [12CO/13CO] abundance ratios of 7.8 − 1.5 + 2.7 and 6.5 − 1.3 + 3.0 at radii of 0.4 kpc and 1 kpc. The emission from the high-density tracers HCN, HCO+, HNC, CS, and CN is also relatively bright, and CN is unusually optically thick in the inner parts of NGC 4526. These features hint that processing in the cluster environment may have removed much of the galaxy’s relatively diffuse, optically thinner molecular gas along with its atomic gas. Angular momentum transfer to the surrounding intracluster medium may also have caused contraction of the disk, magnifying radial gradients such as we find in [13CO/C18O]. More detailed chemical evolution modeling would be interesting in order to explore whether the unusual [12CO/13CO] abundance ratio is entirely an environmental effect or whether it also reflects the relatively old stellar population in this early-type galaxy.

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“…In this paper, we apply this technique to NGC 6946, which has been widely studied due to its active star formation (Schinnerer et al 2007 classify it as a circumnuclear starburst) and its high frequency of SN in the past century (Sauty et al 1998;Meier & Turner 2004;Schinnerer et al 2007;Kennicutt et al 2011;Murphy et al 2011;Botticella et al 2012;Tsai et al 2013;Gorski et al 2018;Eldridge & Xiao 2019;Eibensteiner et al 2022). Among these studies, there have been inconsistent measurements of the galaxy's global SFR, ranging widely from 3 to 12 M e yr −1 , due to the diverse methods of measuring the SFR and the wide range of distances used.…”

Section: Introductionmentioning

confidence: 99%

Spatially Resolved Recent Star Formation History in NGC 6946

Tran,

Williams,

Levesque

et al. 2023

ApJ

1

2

0

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The nearby face-on star-forming spiral galaxy NGC 6946 is known as the Fireworks Galaxy due to its hosting an unusually large number of supernovae. We analyze its resolved near-ultraviolet stellar photometry measured from images taken with the Hubble Space Telescope’s Wide Field Camera 3 with the F275W and F336W filters. We model the color–magnitude diagrams of the UV photometry to derive the spatially resolved star formation history of NGC 6946 over the last 25 Myr. From this analysis, we produce maps of the spatial distribution of the young stellar population and measure the total recent star formation rate (SFR) of nearly the entire young stellar disk. We find the global SFR(age ≤25 Myr) = 13.17 − 0.79 + 0.91 M ⊙ yr − 1 . Over this period, the SFR is initially very high ( 23.39 − 2.11 + 2.43 M ⊙ yr − 1 16–25 Myr ago), then monotonically decreases to 5.31 − 0.17 + 0.19 M ⊙ yr − 1 in the last 10 Myr. This decrease in global SFR over the last 25 Myr is consistent with measurements made with other SFR indicators. We discuss in detail two of the most active regions of the galaxy, which we find are responsible for 3% and 5% of the total star formation over the past 6.3 Myr.

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“…With the establishment of the Atacama Large Millimeter/ submillimeter Array (ALMA), astronomers have started to target lines fainter than the bright CO lines toward nearby galactic cold gas outflows, to inspect their physical and chemical properties (e.g., Aalto et al 2012;Walter et al 2017;Aladro et al 2018;Harada et al 2018;Michiyama et al 2020). Concurrently, unbiased spectral line surveys have begun to show the molecular line richness and diversity in extragalactic systems (e.g., Martín et al 2006;Rangwala et al 2011;Aladro et al 2015;Takano et al 2019;Martín et al 2021;den Brok et al 2022;Eibensteiner et al 2022) as well as in galaxies with known molecular outflow features (e.g., Sakamoto et al 2021).…”

Section: Introductionmentioning

confidence: 99%

AGN-driven Cold Gas Outflow of NGC 1068 Characterized by Dissociation-sensitive Molecules

Tosaki

¹

,

Takano

²

,

Harada

³

et al. 2022

ApJ

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Recent developments in (sub)millimeter facilities have drastically changed the amount of information obtained from extragalactic spectral scans. In this paper, we present a feature extraction technique using principal component analysis (PCA) applied to arcsecond-resolution (1.″0–2.″0 = 72–144 pc) spectral scan data sets for the nearby type-2 Seyfert galaxy NGC 1068, using Band 3 of the Atacama Large Millimeter/submillimeter Array. We apply PCA to 16 well-detected molecular line intensity maps convolved to a common 150 pc resolution. In addition, we include the [S iii]/[S ii] line ratio and [C i] 3 P 1–3 P 0 maps in the literature, both of whose distributions show a remarkable resemblance to that of a kiloparsec-scale biconical outflow from the central active galactic nucleus. We identify two prominent features: (1) central concentration at the circumnuclear disk (CND) and (2) two peaks across the center that coincide with the biconical outflow peaks. The concentrated molecular lines in the CND are mostly high-dipole molecules (e.g., H13CN, HC3N, and HCN). Line emissions from molecules known to be enhanced in an irradiated interstellar medium, CN, C2H, and HNC, show similar concentrations and extended components along the bicone, suggesting that molecule dissociation is a dominant chemical effect of the cold molecular outflow of this galaxy. Although further investigation should be made, this scenario is consistent with the faintness or absence of emission lines from CO isotopologues, CH3OH, and N2H+ in the outflow, which are easily destroyed by dissociating photons and electrons.

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A 2–3 mm high-resolution molecular line survey towards the centre of the nearby spiral galaxy NGC 6946

Cited by 18 publications

References 204 publications

Down but Not Out: Properties of the Molecular Gas in the Stripped Virgo Cluster Early-type Galaxy NGC 4526

Down but Not Out: Properties of the Molecular Gas in the Stripped Virgo Cluster Early-type Galaxy NGC 4526

Spatially Resolved Recent Star Formation History in NGC 6946

AGN-driven Cold Gas Outflow of NGC 1068 Characterized by Dissociation-sensitive Molecules

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