J/ApJ/883/10 3D shapes of extremely metal-poor galaxies (Putko+, 2019)
Inferring the 3D shapes of extremely metal-poor galaxies from sets of projected
shapes.
Putko J., Sanchez Almeida J., Munoz-Tunon C., Asensio Ramos A.,
Elmegreen B.G., Elmegreen D.M.
<Astrophys. J., 883, 10 (2019)>
=2019ApJ...883...10P 2019ApJ...883...10P
ADC_Keywords: Galaxies; Optical; Morphology
Keywords: galaxies: dwarf ; galaxies: evolution ; galaxies: formation ;
galaxies: fundamental parameters ; galaxies: irregular
Abstract:
The three-dimensional (3D) shape of a galaxy inevitably is tied to how
it has formed and evolved and to its dark matter halo. Local extremely
metal-poor galaxies (XMPs; defined as having an average gas-phase
metallicity <0.1 solar) are important objects for understanding galaxy
evolution largely because they appear to be caught in the act of
accreting gas from the cosmic web, and their 3D shape may reflect
this. Here, we report on the 3D shape of XMPs as inferred from their
observed projected minor-to-major axial ratios using a hierarchical
Bayesian inference model, which determines the likely shape and
orientation of each galaxy, while simultaneously inferring the average
shape and dispersion. We selected a sample of 149 XMPs and divided it
into three subsamples according to physical size and found that (1)
the stellar component of XMPs of all sizes tends to be triaxial, with
an intermediate axis ∼0.7 times the longest axis and that (2) smaller
XMPs tend to be relatively thicker, with the shortest axis going from
∼0.15 times the longest axis for the large galaxies to ∼0.4 for the
small galaxies. We provide the inferred 3D shape and inclination of
the individual XMPs in electronic format. We show that our results for
the intermediate axis are not clouded by a selection effect against
face-on XMPs. We discuss how an intermediate axis significantly
smaller than the longest axis may be produced by several mechanisms,
including lopsided gas accretion, non-axisymmetric star formation, or
coupling with an elongated dark matter halo. Large relative thickness
may reflect slow rotation, stellar feedback, or recent gas accretion.
Description:
The galaxies used in our inference of 3D shape are from
Sanchez Almeida+ (2016, J/ApJ/819/110), who mined the spectroscopic
catalog of the Sloan Digital Sky Survey (SDSS) in producing the
largest published sample (195) of extremely metal-poor galaxies (XMPs)
from a single survey.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 72 139 3-D shape parameters for individual galaxies
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See also:
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
J/ApJ/631/85 : Galaxy morphologies in the Hubble UDF (Elmegreen+, 2005)
J/ApJS/162/49 : UBV imaging of irregular galaxies (Hunter+, 2006)
J/ApJ/743/77 : Extremely metal-poor (XMP) gal. in SDSS (Morales-Luis+, 2011)
J/A+A/558/A18 : HI spectra of extremely metal-poor (XMP) gal. (Filho+, 2013)
J/ApJ/772/135 : 3.6um surface brightness from S4G (Zaritsky+, 2013)
J/MNRAS/444/3015 : Morphologies of S4G galaxies (Laine+, 2014)
J/ApJ/819/110 : Extremely metal-poor gal. in SDSS. II. (Sanchez Almeida+ 2016)
J/MNRAS/468/703 : Abell 168 ultra-diffuse galaxies distribution (Roman+, 2017)
http://www.sdss.org/ : SDSS home page
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000) (1)
11- 18 F8.5 deg DEdeg Declination in decimal degrees (J2000) (1)
20- 23 F4.2 --- C [0.14/0.4] Thickness normalized to the axis length
25- 28 F4.2 --- e_C [0.03/0.06] The 16th percentile uncertainty in C
30- 33 F4.2 --- E_C [0.02/0.09] The 84th percentile uncertainty in C
35- 38 F4.2 --- B [0.66/0.72] Width
40- 43 F4.2 --- e_B [0.04/0.1] The 16th percentile uncertainty in B
45- 48 F4.2 --- E_B [0.04/0.1] The 84th percentile uncertainty in B
50- 54 F5.2 deg Inc [33/86] Inclination of major axis with
respect to the line-of-sight
56- 60 F5.2 deg e_Inc [4/26] The 16th percentile uncertainty in Inc
62- 66 F5.2 deg E_Inc [2/27] The 84th percentile uncertainty in Inc
68- 68 A1 --- Set Sub-sample (2)
70- 72 I3 --- ID [1/195] Sanchez Almeida+ 2016, J/ApJ/819/110
identifier
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Note (1): The full table contains 139 galaxies divided among our three
sub-samples. It is sorted by sub-sample and then by R.A.
Note (2): Figure 3 shows how sub-samples are divided. The family parameters
are described in Section 2.3 and Table 2. Code as follows:
S = Small (µB=0.39±0.02, µB=0.71±0.05 ; 54 occurrences)
M = Medium (µB=0.26±0.04, µB=0.66±0.03 ; 54 occurrences)
L = Large (µB=0.16±0.03, µB=0.71±0.08 ; 31 occurrences)
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 22-Feb-2021