Quasars with PV broad absorption in BOSS data release 9 [GA]


Broad absorption lines (BALs) found in a significant fraction of quasar spectra identify high-velocity outflows that might be present in all quasars and could be a major factor in feedback to galaxy evolution. Understanding the nature of these flows requires further constraints on their physical properties, including their column densities, for which well-studied BALs, such as CIV 1548,1551, typically provide only a lower limit because of saturation effects. Low-abundance lines, such as PV 1118,1128, indicate large column densities, implying outflows more powerful than measurements of CIV alone would indicate. We search through a sample of 2694 BAL quasars from the SDSS-III/BOSS DR9 quasar catalog for such absorption, and we identify 81 definite' and 86probable’ detections of PV broad absorption, yielding a firm lower limit of 3.0-6.2% for the incidence of such absorption among BAL quasars. The PV-detected quasars tend to have stronger CIV and SiIV absorption, as well as a higher incidence of LoBAL absorption, than the overall BAL quasar population. Many of the PV-detected quasars have CIV troughs that do not reach zero intensity (at velocities where PV is detected), confirming that the outflow gas only partially covers the UV continuum source. PV appears significantly in a composite spectrum of non-PV-detected BAL quasars, indicating that PV absorption (and large column densities) are much more common than indicated by our search results. Our sample of PV detections significantly increases the number of known PV detections, providing opportunities for follow-up studies to better understand BAL outflow energetics.

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D. Capellupo, F. Hamann, H. Herbst, et. al.
Wed, 26 Apr 17

Comments: 18 pages, 12 figures. All spectral plots available at this http URL

Chemodynamical Modelling of the Galactic Bulge and Bar [GA]


We present the first self-consistent chemodynamical model fitted to reproduce data for the galactic bulge, bar and inner disk. We extend the Made-to-Measure method to an augmented phase-space including the metallicity of stars, and show its first application to the bar region of the Milky Way. Using data from the ARGOS and APOGEE (DR12) surveys, we adapt the recent dynamical model from Portail et al. to reproduce the observed spatial and kinematic variations as a function of metallicity, thus allowing the detailed study of the 3D density distributions, kinematics and orbital structure of stars in different metallicity bins. We find that metal-rich stars with [Fe/H] > -0.5 are strongly barred and have dynamical properties that are consistent with a common disk origin. Metal-poor stars with [Fe/H] < -0.5 show strong kinematic variations with metallicity, indicating varying contributions from the underlying stellar populations. Outside the central kpc, metal-poor stars are found to have the density and kinematics of a thick disk while in the inner kpc, evidence for an extra concentration of metal-poor stars is found. Finally, the combined orbit distributions of all metallicities in the model naturally reproduce the observed vertex deviations in the bulge. This paper demonstrates the power of Made-to-Measure chemodynamical models, that when extended to other chemical dimensions will be very powerful tools to maximize the information obtained from large spectroscopic surveys such as APOGEE, GALAH and MOONS.

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M. Portail, C. Wegg, O. Gerhard, et. al.
Wed, 26 Apr 17

Comments: Paper submitted to MNRAS, this version after response to referee report. 20 pages, 17 figures

An Estimation of the Star Formation Rate in the Perseus Complex [GA]


We present the results of our investigation of the star-forming potential in the Perseus star-forming complex. We build on previous starless core, protostellar core, and young stellar object (YSO) catalogs from Spitzer, Herschel, and SCUBA observations in the literature. We place the cores and YSOs within seven star-forming clumps based on column densities greater than 5×10^21 cm^-2. We calculate the mean density and free-fall time for 69 starless cores as 5.55×10^-19 gcm^-3 and 0.1 Myr,respectively, and we estimate the star formation rate for the near future as 150 Msun Myr^-1. According to Bonnor Ebert stability analysis, we find that majority of starless cores in Perseus are unstable. Broadly, these cores can collapse to form the next generation of stars. We found a relation between starless cores and YSOs, where the numbers of young protostars (Class 0 + Class I) are similar to the numbers of starless cores. This similarity, which shows a one-to-one relation, suggests that these starless cores may form the next generation of stars with approximately the same formation rate as the current generation, as identified by the Class 0 and Class I protostars. It follows that if such a relation between starless cores and any YSO stage exists, the SFR values of these two populations must be nearly constant. In brief, we propose that this one-to-one relation is an important factor in better understanding the star formation process within a cloud.

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S. Mercimek, P. Myers, K. Lee, et. al.
Wed, 26 Apr 17

Comments: Published in AJ, 2017, 153, 214; 14 pages, 7 figures

Extreme submillimetre starburst galaxies [GA]


We use two catalogues, a Herschel catalogue selected at 500 mu (HerMES) and an IRAS catalogue selected at 60 mu (RIFSCz), to contrast the sky at these two wavelengths.
Both surveys demonstrate the existence of extreme starbursts, with star-formation rates (SFRs) > 5000 Msun/yr. There appears to be a maximum (un-lensed) star-formation rate of 30,000 Msun/yr. IRAS sources with estimates higher than this are either lensed systems, blazars, or erroneous photometric redshifts.
At redshifts 3 to 5, the time-scale for the Herschel galaxies to make their current mass of stars at their present rate of formation ~ 10^8 yrs, so these galaxies are making a significant fraction of their stars in the current star-formation episode. Using dust mass as a proxy for gas mass, the Herschel galaxies at redshift 3 to 5 have gas masses comparable to their mass in stars.
We have plotted here the individual spectral energy distributions (SEDs) for the 58 extreme starbursts in our Herschel survey, for which we have more complete SED information. Over 50% are QSOs or have an AGN dust torus, i.e. are Type 2 AGN, but in all cases the infrared luminosity is dominated by a starburst component. We derive a mean covering factor for AGN dust as a function of redshift and derive black hole masses and black hole accretion rates. There is a universal ratio of black-hole mass to stellar mass, ~ 10^{-3}, driven by the strong period of star-formation and black-hole growth at z = 1-5.

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M. Rowan-Robinson, L. Wang, D. Farrah, et. al.
Wed, 26 Apr 17

Comments: 13 pages, 21 figures, submitted to MNRAS

Yonsei evolutionary population synthesis (YEPS). II. Spectro-photometric evolution of helium-enhanced stellar populations [GA]


The discovery of multiple stellar populations in the Milky Way globular clusters (GCs) has stimulated various follow-up studies on helium-enhanced stellar populations. Here, we present the evolutionary population synthesis models for spectro-photometric evolution of simple stellar populations (SSPs) with varying initial helium abundance ($Y_{ini}$). We show that $Y_{ini}$ brings about dramatic changes in spectro-photometric properties of SSPs. Like the normal-helium SSPs, the integrated spectro-photometric evolution of helium-enhanced SSPs is also dependent on metallicity and age for a given $Y_{ini}$. We discuss the implications and the prospects for the helium-enhanced populations in relation to the second generation populations found in the Milky Way GCs. All models are available at \url{this http URL}.

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C. Chung, S. Yoon and Y. Lee
Wed, 26 Apr 17

Comments: Accepted for publication in ApJ, 20 pages, 12 figures, 3 tables

The Emission Structure of Formaldehyde MegaMasers [GA]


The formaldehyde MegaMaser emission has been mapped for the three host galaxies IC\,860. IRAS\,15107$+$0724, and Arp\,220. Elongated emission components are found at the nuclear centres of all galaxies with an extent ranging between 30 to 100 pc. These components are superposed on the peaks of the nuclear continuum. Additional isolated emission components are found superposed in the outskirts of the radio continuum structure. The brightness temperatures of the detected features ranges from 0.6 to 13.4 $\times 10^{4}$ K, which confirms their masering nature. The masering scenario is interpreted as amplification of the radio continuum by foreground molecular gas that is pumped by far-infrared radiation fields in these starburst environments of the host galaxies.

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W. Baan, T. An, H. Klockner, et. al.
Tue, 25 Apr 17

Comments: Accepted MNRAS

The Intrinsic Far-infrared Continua of Type-1 Quasars [GA]


The range of currently proposed active galactic nucleus (AGN) far-infrared templates results in uncertainties in retrieving host galaxy information from infrared observations and also undermines constraints on the outer part of the AGN torus. We discuss how to test and reconcile these templates. Physically, the fraction of the intrinsic AGN IR-processed luminosity compared with that from the central engine should be consistent with the dust-covering factor. In addition, besides reproducing the composite spectral energy distributions (SEDs) of quasars, a correct AGN IR template combined with an accurate library of star-forming galaxy templates should be able to reproduce the IR properties of the host galaxies, such as the luminosity-dependent SED shapes and aromatic feature strengths. We develop tests based on these expected behaviors and find that the shape of the AGN intrinsic far-IR emission drops off rapidly starting at $\sim20~\mu$m and can be matched by an Elvis et al. (1994)-like template with minor modification. Despite the variations in the near- to mid-IR bands, AGNs in quasars and Seyfert galaxies have remarkably similar intrinsic far-IR SEDs at $\lambda \sim 20$-$100~\mu$ m, suggesting similar emission character of the outermost region of the circumnuclear torus. The variations of the intrinsic AGN IR SEDs among the type-1 quasar population can be explained by the changing relative strengths of four major dust components with similar characteristic temperatures, and there is evidence for compact AGN-heated dusty structures at sub-kpc scales in the far-IR.

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J. Lyu and G. Rieke
Tue, 25 Apr 17

Comments: Accepted for publication in ApJ, 14 pages, 9 figures, 5 tables. The quasar intrinsic IR templates can be found at this http URL or in the published paper