New insights in the mid-infrared bubble N49 site: a clue of collision of filamentary molecular clouds [GA]

We investigate the star formation processes operating in a mid-infrared bubble N49 site, which harbors an O-type star in its interior, an ultracompact HII region, and a 6.7 GHz methanol maser at its edges. The 13CO line data reveal two velocity components (at velocity peaks ~88 and ~95 km/sec) in the direction of the bubble. An elongated filamentary feature (length >15 pc) is investigated in each molecular cloud component, and the bubble is found at the interface of these two filamentary molecular clouds. The Herschel temperature map traces all these structures in a temperature range of ~16-24 K. In the velocity space of 13CO, the two molecular clouds are separated by ~7 km/sec, and are interconnected by a lower intensity intermediate velocity emission (i.e. a broad bridge feature). A possible complementary molecular pair at [87, 88] km/sec and [95, 96] km/sec is also observed in the velocity channel maps. These observational signatures are in agreement with the outcomes of simulations of the cloud-cloud collision process. There are also noticeable embedded protostars and Herschel clumps distributed toward the filamentary features including the intersection zone of the two molecular clouds. In the bubble site, different early evolutionary stages of massive star formation are also present. Together, these observational results suggest that in the bubble N49 site, the collision of the filamentary molecular clouds appears to be operated about 0.7 Myr ago, and may have triggered the formation of embedded protostars and massive stars.

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L. Dewangan, D. Ojha and I. Zinchenko
Mon, 20 Nov 17

Comments: 19 pages, 11 figures, 2 tables. Accepted for publication in The Astrophysical Journal

Stellar population properties for 2 million galaxies from SDSS DR14 and DEEP2 DR4 from full spectral fitting [GA]

We determine the stellar population properties – age, metallicity, dust reddening, stellar mass and the star formation history – for all spectra classified as galaxies that were published by the Sloan Digital Sky Survey (SDSS data release 14) and by the DEEP2 (data release 4) galaxy surveys. We perform full spectral fitting on individual spectra, making use of high spectral resolution stellar population models. Calculations are carried out for several choices of the model input, including three stellar initial mass functions and three input stellar libraries to the models. We study the accuracy of parameter derivation, in particular the stellar mass, as a function of the signal-to-noise of the galaxy spectra. We find that signal to noise ratio per pixel around 20 (5) allow a statistical accuracy on $\log_{10}(M^{*}/M_{\odot})$ of 0.2 (0.4) dex, for the Chabrier IMF. We obtain the galaxy stellar mass function probed by SDSS, eBOSS and DEEP2 for galaxies with $0.2<z<0.8$. We study DEEP2 galaxies selected by their \OII luminosity in the redshift range $0.83<z<1.03$, finding that they have stellar masses with a flat number density in the range $10^9<M/M_{\odot}<10^{11.5}$. We publish all catalogs of properties as well as model spectra of the continuum for these galaxies as a value added catalog of the fourteenth data release of the SDSS. This catalog is about twice as large as its predecessors (DR12) and will hopefully aid a variety of studies on galaxy evolution and cosmology.

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J. Comparat, C. Maraston, D. Goddard, et. al.
Mon, 20 Nov 17

Comments: 13 pages, 6 figures, submitted to A&A. The corresponding SDSS value-added catalog is available at this http URL

A possible binary AGN in Mrk\,622? [GA]

Mrk\,622 is a Compton Thick AGN and a double-peaked narrow emission line galaxy, thus a dual AGN candidate. In this work, new optical long-slit spectroscopic observations clearly show that this object is rather a triple peaked narrow emission line galaxy, with both blue and red shifted narrow emission lines, as well as a much narrower emission line centred at the host galaxy systemic velocity. The average velocity offset between the blue and red shifted components is $\sim$500 km\,s$^{-1}$, which is producing the apparent double-peaked emission lines. These two components are in the loci of AGN in the Baldwin, Phillips \& Terlevich (BPT) diagrams and are found to be spatially separated by $\sim$76 pc. Analysis of the optical spatially resolved spectroscopic observations presented in this work favours that Mrk\,622 is a system consisting of a Composite AGN amidst a binary AGN candidate, likely the result of a recent merger. This notwithstanding, outflows from a starburst, or single AGN could also explain the triple nature of the emission lines.

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E. Benitez, J. Rodriguez-Espinosa, I. Cruz-Gonzalez, et. al.
Mon, 20 Nov 17

Comments: 5 pages, 3 figures, 3 tables. Accepted in MNRAS Letters. 5 pages, 3 tables, 3 figures

Occurrence of LINER galaxies within the galaxy group environment [GA]

We study the properties of a sample of 3967 LINER galaxies selected from SDSS-DR7, respect to their proximity to galaxy groups. The host galaxies of LINER have been analysed and compared with a well defined control sample of 3841 non-LINER galaxies matched in redshift, luminosity, colour, morphology, age and stellar mass content. We find no difference between LINER and control galaxies in terms of colour and age of stellar population as function of the virial mass and distance to the geometric centre of the group. However, we find that LINER are more likely to populate low density environments in spite of their morphology, which is typical of high density regions such as rich galaxy clusters. For rich (poor) galaxy groups, the occurrence of LINER is $\sim$2 times lower (higher) than the occurrence of matched, non-LINER galaxies. Moreover, LINER hosts do not seem to follow the expected morphology-density relation in groups of high virial mass. The high frequency of LINERS in low density regions could be due to the combination of a sufficiently ample gas reservoir to power the low ionization emission and/or enhanced galaxy interaction rates benefiting the gas flow toward their central regions.

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G. Coldwell, L. Pereyra, S. Alonso, et. al.
Mon, 20 Nov 17

Comments: Published in MNRAS, 10 pages, 7 figures

First Extended Catalogue of Galactic Bubbles InfraRed Fluxes from WISE and Herschel Surveys [GA]

In this paper, we present the first extended catalogue of far-infrared fluxes of Galactic bubbles. Fluxes were estimated for 1814 bubbles, defined here as the `golden sample’, and were selected from the Milky Way Project First Data Release (Simpson et al.) The golden sample was comprised of bubbles identified within the Wide-field Infrared Survey Explorer (WISE) dataset (using 12- and 22-$\mu$m images) and Herschel data (using 70-, 160-, 250-, 350- and 500-$\mu$m wavelength images). Flux estimation was achieved initially via classical aperture photometry and then by an alternative image analysis algorithm that used active contours. The accuracy of the two methods was tested by comparing the estimated fluxes for a sample of bubbles, made up of 126 H II regions and 43 planetary nebulae, which were identified by Anderson et al. The results of this paper demonstrate that a good agreement between the two was found. This is by far the largest and most homogeneous catalogue of infrared fluxes measured for Galactic bubbles and it is a step towards the fully automated analysis of astronomical datasets.

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F. Bufano, P. Leto, D. Carey, et. al.
Mon, 20 Nov 17

Comments: 22 pages, 16 figures, 10 tables, published on MNRAS

Investigating the radial acceleration relation in early-type galaxies using the Jeans analysis [GA]

Investigating the gravitational field in the early-type galaxies (ETGs, i.e. ellipticals and lenticulars) up to large radii is observationally difficult. It is questionable how the radial acceleration (RAR) in the ETGs looks like, i.e. the relation between the dynamically inferred gravitational acceleration and the acceleration expected from the distribution of the visible matter. This relation is nearly universal for the spiral galaxies, in agreement with the MOND modified dynamics paradigm. In this contribution, we investigate a sample of 15 ETGs. We extract their full kinematic profiles out to several effective radii from their globular cluster systems and estimate their gravitational field using the Jeans equation. We parametrize the gravitational field by that produced by the stars and a Navarro-Frenk-White DM halo. We find that only a 4-5 of our ETGs follow the RAR for the spiral galaxies. All these galaxies are fast rotators, have disky isophotes, appear mostly very elongated and the have bluest colors in our sample. This suggests that they might be spiral galaxies which lost their gas. Our galaxies deviating from the RAR for the spirals either disprove MOND, contain unobserved matter, or indicate a flaw in the method.

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M. Bilek and S. Samurovic
Mon, 20 Nov 17

Comments: 6 pages, 1 figure, 1 table. This is an updated and expanded version of the submitted contribution to the Proceedings of the 18th Serbian Astronomical Conference held in Belgrade 17-21 October 2017 (original title “Two types of dark matter distribution in early-type galaxies”)

Joint NuSTAR and Chandra analysis of the obscured quasar in IC 2497 – Hanny's Voorwerp system [GA]

We present new NuSTAR observations of the core of IC 2497, the galaxy associated with Hanny’s Voorwerp. The combined fits of the Chandra (0.5-8 keV) and NuSTAR (3-24 keV) X-ray spectra, together with WISE mid-IR photometry, optical longslit spectroscopy and optical narrowband imaging, suggest that the galaxy hosts a Compton-thick AGN ($N_{\rm H} \sim 2 \times 10^{24}$ cm$^{-2}$, current intrinsic luminosity $L_{\rm bol} \sim 2-5 \times 10^{44}$ erg s$^{-1}$) whose luminosity dropped by a factor $\sim 50$ within the last $\sim 100$ kyr. This corresponds to a change in Eddington ratio from $\rm \lambda_{Edd} \sim 0.06$ to $\rm \lambda_{Edd} \sim 0.001$. We argue that the AGN in IC 2497 should not be classified as a changing-look AGN, but rather we favour the interpretation where the AGN is undergoing a change in accretion state (from radiatively efficient to radiatively inefficient). In this scenario the observed drop in luminosity and Eddington ratio corresponds to the final stage of an AGN accretion phase. Our results are consistent with previous studies in the optical, X-ray and radio although the magnitude of the drop is lower than previously suggested. In addition, we discuss a possible analogy between X-ray binaries and AGN.

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L. Sartori, K. Schawinski, M. Koss, et. al.
Mon, 20 Nov 17

Comments: 9 pages, 3 figures. Accepted for publication in MNRAS