scholarly journals Broad line emission in dwarf galaxies: the first detection of low-metallicity AGN

2008 ◽  
Vol 4 (S255) ◽  
pp. 370-374
Author(s):  
Yuri I. Izotov
Keyword(s):  
Dwarf Galaxies ◽  
Line Emission ◽  
Sloan Digital Sky Survey ◽  
Strongly Correlated ◽  
Collisional Excitation ◽  
Sky Survey ◽  
Balmer Lines ◽  
Low Metallicity ◽  
Low Mass ◽  
High Metallicity

AbstractObservations of AGN show that they generally possess a high metallicity, varying from solar to supersolar metallicities. This is the case since AGN are usually found in massive, bulge-dominated galaxies that have converted most of their gas into stars by the present epoch. Since AGN metallicity is strongly correlated with stellar mass, low-metallicity AGN are expected to be in low-mass dwarf galaxies. However, until now, searches in low-mass galaxies have only turned up AGN with metallicities around half that of typical AGN, i.e. with solar or slightly subsolar values. We report the discovery of four low-metallicity dwarf galaxies in the Data Release 6 of the Sloan Digital Sky survey, with 12 + log O/H in the range 7.4–8.0, and that appear to harbor an AGN. In the course of a long-range program to search for extremely metal-deficient emission-line dwarf galaxies, we have come across four galaxies with very unusual spectra: the strong permitted emission lines, mainly the Hα line, show very prominent broad components, with full widths at zero intensity corresponding to velocities varying between 2200 and 3500 km s−1, and extraordinarily large broad Hα luminosities, varying from 3×1041 to 2×1042 erg s−1. The Balmer lines show a very steep decrement, suggesting collisional excitation and that the broad emission comes from very dense gas (Ne ≫ 104 cm−3). Only the presence of an accretion disk around an intermediate-mass black hole in the dwarf galaxies appears to account for these properties.

scholarly journals Are sdAs helium core stars?

2017 ◽  
Vol 26 (1) ◽  
Author(s):  
Ingrid Pelisoli ◽  
S. O. Kepler ◽  
Detlev Koester
Keyword(s):  
Main Sequence ◽  
Galactic Disk ◽  
Physical Nature ◽  
Sloan Digital Sky Survey ◽  
Distance Modulus ◽  
Main Sequence Stars ◽  
Sky Survey ◽  
Balmer Lines ◽  
Low Mass ◽  
Binary Evolution

AbstractEvolved stars with a helium core can be formed by non-conservative mass exchange interaction with a companion or by strong mass loss. Their masses are smaller than 0.5 M⊙. In the database of the Sloan Digital Sky Survey (SDSS), there are several thousand stars which were classified by the pipeline as dwarf O, B and A stars. Considering the lifetimes of these classes on the main sequence, and their distance modulus at the SDSS bright saturation, if these were common main sequence stars, there would be a considerable population of young stars very far from the galactic disk. Their spectra are dominated by Balmer lines which suggest effective temperatures around 8 000-10 000 K. Several thousand have significant proper motions, indicative of distances smaller than 1 kpc. Many show surface gravity in intermediate values between main sequence and white dwarf, 4.75 < log g < 6.5, hence they have been called sdA stars. Their physical nature and evolutionary history remains a puzzle. We propose they are not H-core main sequence stars, but helium core stars and the outcomes of binary evolution. We report the discovery of two new extremely-low mass white dwarfs among the sdAs to support this statement.

scholarly journals Star formation in low-redshift cluster dwarf galaxies

2020 ◽  
Vol 493 (4) ◽  
pp. 5625-5635
Author(s):  
Cody M Rude ◽  
Madina R Sultanova ◽  
Gihan L Ipita Kaduwa Gamage ◽  
Wayne A Barkhouse ◽  
Sandanuwan P Kalawila Vithanage
Keyword(s):  
Star Formation ◽  
Dwarf Galaxies ◽  
Sloan Digital Sky Survey ◽  
Galaxy Interactions ◽  
Cluster Data ◽  
Luminosity Functions ◽  
Sky Survey ◽  
Ram Pressure ◽  
Low Mass ◽  
Central Concentration

ABSTRACT Evolution of galaxies in dense environments can be affected by close encounters with neighbouring galaxies and interactions with the intracluster medium. Dwarf galaxies (dGs) are important as their low mass makes them more susceptible to these effects than giant systems. Combined luminosity functions (LFs) in the r and u band of 15 galaxy clusters were constructed using archival data from the Canada–France–Hawaii Telescope. LFs were measured as a function of clustercentric radius from stacked cluster data. Marginal evidence was found for an increase in the faint-end slope of the u-band LF relative to the r-band with increasing clustercentric radius. The dwarf-to-giant ratio (DGR) was found to increase toward the cluster outskirts, with the u-band DGR increasing faster with clustercentric radius compared to the r-band. The dG blue fraction was found to be ∼2 times larger than the giant galaxy blue fraction over all clustercentric distance (∼5σ level). The central concentration (C) was used as a proxy to distinguish nucleated versus non-nucleated dGs. The ratio of high-C to low-C dGs was found to be ∼2 times greater in the inner cluster region compared to the outskirts (2.8σ level). The faint-end slope of the r-band LF for the cluster outskirts (0.6 ≤ r/r200 &lt; 1.0) is steeper than the Sloan Digital Sky Survey field LF, while the u-band LF is marginally steeper at the 2.5σ level. Decrease in the faint-end slope of the r- and u-band cluster LFs towards the cluster centre is consistent with quenching of star formation via ram pressure stripping and galaxy–galaxy interactions.

scholarly journals Spitzer IRS Observations of Low-Mass Seyfert Galaxies

2009 ◽  
Vol 5 (S267) ◽  
pp. 268-268
Author(s):  
Carol E. Thornton ◽  
Aaron J. Barth ◽  
Luis C. Ho ◽  
Jenny E. Greene
Keyword(s):  
Dust Emission ◽  
Seyfert Galaxies ◽  
Sloan Digital Sky Survey ◽  
Physical Conditions ◽  
Sky Survey ◽  
Low Mass ◽  
Ngc 4395 ◽  
Black Hole Masses

The Sloan Digital Sky Survey has made it possible to identify the first samples of active galaxies with estimated black hole masses below ~ 106M⊙. We have obtained Spitzer IRS low-resolution spectra, covering 5–38 μm, of a sample of 41 Seyfert galaxies with low-mass black holes. Our sample includes SDSS-selected objects from the low-mass Seyfert 1 sample of Greene & Ho (2004) and the low-mass Seyfert 2 sample of Barth et al. (2008), as well as NGC 4395 and POX 52. The goals of this work are to examine the dust emission properties of these objects and investigate the relationship between type 1 and type 2 AGNs at low luminosities and low masses, to search for evidence of star formation, and to use emission-line diagnostics to constrain physical conditions within the narrow-line regions. Here we present preliminary results from this project.

scholarly journals White Dwarf Stars

2017 ◽  
Vol 45 ◽  
pp. 1760023
Author(s):  
S. O. Kepler ◽  
Alejandra Daniela Romero ◽  
Ingrid Pelisoli ◽  
Gustavo Ourique
Keyword(s):  
White Dwarf ◽  
Final Stage ◽  
White Dwarfs ◽  
Sloan Digital Sky Survey ◽  
Dwarf Stars ◽  
Multiple Systems ◽  
White Dwarf Stars ◽  
Sky Survey ◽  
Data Release ◽  
Low Mass

White dwarf stars are the final stage of most stars, born single or in multiple systems. We discuss the identification, magnetic fields, and mass distribution for white dwarfs detected from spectra obtained by the Sloan Digital Sky Survey up to Data Release 13 in 2016, which lead to the increase in the number of spectroscopically identified white dwarf stars from 5[Formula: see text]000 to 39[Formula: see text]000. This number includes only white dwarf stars with [Formula: see text], i.e., excluding the Extremely Low Mass white dwarfs, which are necessarily the byproduct of stellar interaction.

scholarly journals Mg II λ2797, λ2803 emission in a large sample of low-metallicity star-forming galaxies from SDSS DR14

2019 ◽  
Vol 624 ◽  
pp. A21 ◽  
Author(s):  
N. G. Guseva ◽  
Y. I. Izotov ◽  
K. J. Fricke ◽  
C. Henkel
Keyword(s):  
Noble Gas ◽  
Formation Rate ◽  
Sloan Digital Sky Survey ◽  
Large Sample ◽  
Star Forming ◽  
Magnesium Depletion ◽  
Sky Survey ◽  
Solar Metallicity ◽  
Low Metallicity ◽  
Damped Lyman Alpha Systems

A large sample of Mg II emitting star-forming galaxies with low metallicity [O/H] = log(O/H) – log(O/H)⊙ between –0.2 and –1.2 dex is constructed from Data Release 14 of the Sloan Digital Sky Survey. We selected 4189 galaxies with Mg II λ2797, λ2803 emission lines in the redshift range z ∼ 0.3–1.0 or 35% of the total Sloan Digital Sky Survey star-forming sample with redshift z ≥ 0.3. We study the dependence of the magnesium-to-oxygen and magnesium-to-neon abundance ratios on metallicity. Extrapolating this dependence to [Mg/Ne] = 0 and to solar metallicity we derive a magnesium depletion of [Mg/Ne] ≃ –0.4 (at solar metallicity). We prefer neon instead of oxygen to evaluate the magnesium depletion in the interstellar medium because neon is a noble gas and is not incorporated into dust, contrary to oxygen. Thus, we find that more massive and more metal abundant galaxies have higher magnesium depletion. The global parameters of our sample, such as the mass of the stellar population and star formation rate, are compared with previously obtained results from the literature. These results confirm that Mg II emission has a nebular origin. Our data for interstellar magnesium-to-oxygen abundance ratios relative to the solar value are in good agreement with similar measurements made for Galactic stars, for giant stars in the Milky Way satellite dwarf galaxies, and with low-metallicity damped Lyman-alpha systems.

PERIODIC VARIABILITY OF LOW-MASS STARS IN SLOAN DIGITAL SKY SURVEY STRIPE 82

2011 ◽  
Vol 731 (1) ◽  
pp. 17 ◽  
Author(s):  
A. C. Becker ◽  
J. J. Bochanski ◽  
S. L. Hawley ◽  
Ž. Ivezić ◽  
A. F. Kowalski ◽  
...  
Keyword(s):  
Sloan Digital Sky Survey ◽  
Low Mass Stars ◽  
Sky Survey ◽  
Low Mass

scholarly journals LOW-MASS SEYFERT 2 GALAXIES IN THE SLOAN DIGITAL SKY SURVEY

2008 ◽  
Vol 136 (3) ◽  
pp. 1179-1200 ◽  
Author(s):  
Aaron J. Barth ◽  
Jenny E. Greene ◽  
Luis C. Ho
Keyword(s):  
Sloan Digital Sky Survey ◽  
Sky Survey ◽  
Low Mass

scholarly journals The population of galaxies that contribute to the H i mass function

2020 ◽  
Vol 494 (2) ◽  
pp. 2664-2678 ◽  
Author(s):  
Saili Dutta ◽  
Nishikanta Khandai ◽  
Biprateep Dey
Keyword(s):  
Total Sample ◽  
Mass Function ◽  
Sloan Digital Sky Survey ◽  
Density Parameter ◽  
Total Contribution ◽  
Sky Survey ◽  
Low Mass ◽  
Different Populations ◽  
Galaxy Populations ◽  
Definition Of

ABSTRACT We look at the contribution of different galaxy populations to the atomic hydrogen (H i) mass function (HIMF) and the H i density parameter, ΩH i, in the local Universe. Our analysis is based on a sample of 7857 H i selected galaxies selected from a volume common to the Sloan Digital Sky Survey (SDSS) and Arecibo Fast Legacy ALFA (40 per cent catalogue – α.40) surveys. We define different populations of galaxies in the colour (u − r)–magnitude (Mr) plane and compute the HIMF for each of them. Additionally we compute the HIMF for dark galaxies; these are undetected in SDSS and represent $\sim 2{{\ \rm per\ cent}}$ of the total sample. We find that the luminous red population dominates the total HIMF for $\log _{10}(M_{\rm{H\,{\small I}}}h^2_{70}/M_{\odot }) \ge 10.4$. The full red population – luminous and faint – represents about $\sim 17{{\ \rm per\ cent}}$ of the ΩH i budget, while that of the dark population is $\sim 3{{\ \rm per\ cent}}$. The HIMF about the knee, $\log _{10}(M_{\rm{H\,{\small I}}}h^2_{70}/M_{\odot }) \in [8,10.4]$, is dominated by the faint and luminous blue populations, the latter dominating at larger masses in this interval. Their total contribution to ΩH i is $\sim 55\!-\!70{{\ \rm per\ cent}}$, the variation depending on the definition of population. The dominant populations at the low-mass end, $\log _{10}(M_{\rm{H\,{\small I}}}h^2_{70}/M_{\odot }) \le 8.0$ are the faint blue and faint bluer populations, the latter’s dominance being sensitive to its definition. The full blue (blue–bluer luminous and faint) population represents $\sim 80{{\ \rm per\ cent}}$ of ΩH i. A bimodal HIMF suggested by our results is however not seen since the amplitude of the HIMF of the luminous red population is small compared to that of the luminous blue population.

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