J/ApJ/853/114 Vertical population gradients in NGC 891. I. (Eigenbrot+, 2018)
Vertical population gradients in NGC 891.
I. ∇Pak instrumentation and spectral data.
Eigenbrot A., Bershady M.A.
<Astrophys. J., 853, 114 (2018)>
=2018ApJ...853..114E 2018ApJ...853..114E
ADC_Keywords: Galaxies, spectra; Spectroscopy; Spectra, optical
Keywords: galaxies: individual (NGC 891); galaxies: spiral;
galaxies: stellar content; instrumentation: spectrographs
Abstract:
We have measured vertical and radial stellar population gradients in
NGC 891. We compare these gradients to those known for the Milky Way
from studies of resolved stars. Optical spectroscopic measurements
extend spatially from the disk midplane up to 2.6kpc in height and out
to a radius of 12kpc on both sides of the galaxy. Data were acquired
with ∇Pak, a variable-pitch fiber integral field unit (IFU) on
the WIYN telescope. We describe the laboratory and on-sky performance
of ∇Pak, as well as modifications to the standard observational
and analysis procedures necessary to calibrate data taken with this
unique IFU. ∇Pak has a mean throughput of 80% at 5500Å. To
achieve an estimated precision of 10% in light-weighted mean age and
metallicity, we define a set of spatial apertures in radius and height
in which spectra are binned to achieve a signal-to-noise ratio of
∼20Å-1. We use spectral indices to measure age, metallicity, and
abundance, indicating that NGC 891's stellar populations have
0.2<Z/Z☉<1 and +0.2dex α-enhancement on average. We find a
clear transition from young (<3-5Gyr) to old (>7Gyr) stellar
populations at 0.4kpc, roughly the scale height of the thin disk. We
also find a slight trend toward younger populations at larger radii,
consistent with flaring in an inside-out disk formation scenario. The
vertical age gradient in NGC 891 is in remarkable qualitative
agreement with a model for disk heating tuned to studies of the Milk
Way's solar cylinder.
Description:
Observations of NGC 891 were obtained over two runs in 2014 November
and December using the ∇Pak (GradPak) IFU coupled to the WIYN
Bench Spectrograph. See section 4.
Objects:
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RA (ICRS) DE Designation(s)
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02 22 32.91 +42 20 53.9 NGC 891 = LEDA 9031
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table5.dat 74 261 Data apertures
table6.dat 54 261 Velocity and radial data
table8.dat 64 261 NGC 891 index measurements
table9.dat 47 109 ∇ Pak fiber locations and lab data
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See also:
III/211 : Keck/HIRES Sky Line Atlas (Osterbrock+ 1997)
III/232 : STELIB: library of R∼2000 stellar spectra (Le Borgne+, 2003)
J/ApJS/111/377 : Hγ & Hδ absorption features (Worthey+ 1997)
J/MNRAS/371/703 : MILES library of empirical spectra (Sanchez-Blazquez+, 2006)
J/ApJ/653/1027 : TKRS/GOODS-N Field galaxies (Weiner+, 2006)
J/MNRAS/386/715 : Absorption-line strengths in Coma galaxies (Trager+, 2008)
J/MNRAS/396/1231 : Astrophotometric catalogue of NGC 891 (Rejkuba+, 2009)
J/ApJ/706/1364 : SINS survey of high-z galaxies (Forster Schreiber+, 2009)
J/AJ/137/4377 : List of SEGUE plate pairs (Yanny+, 2009)
J/A+A/565/A4 : NGC 891 70-500um images (Hughes+, 2014)
J/A+A/575/A17 : NGC 891 Herschel PACS and SPIRE spectroscopy (Hughes+, 2015)
J/A+A/581/A103 : CALIFA survey across the Hubble sequence (Gonzalez+, 2015)
J/ApJS/219/15 : Morphologies of z=0-10 galaxies with HST (Shibuya+, 2015)
J/ApJ/832/118 : Emission-line spectroscopy in NGC 891 (Boettcher+, 2016)
J/ApJ/823/114 : The Cannon: a new approach to determine masses (Ness+, 2016)
Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1 I1 --- P [1/6] Pointing
3- 4 I2 --- Ap [1/60] Aperture
6- 8 I3 um Core [200/600] Fiber core diameter
10- 11 I2 --- N [1/15] Number of individual fibers in aperture
13- 52 A40 --- Fiber Fiber ID's in aperture; comma-separated
54- 59 F6.2 --- SNR [13.7/108] Signal-to-noise
61- 66 F6.2 kpc rproj [-11/9] Projected radius
68- 72 F5.2 kpc Z [-0.3/2.4] Height above midplane
74 A1 --- Flag Quality flag (g=high-quality spectra) (1)
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Note (1): Quality flag as follows:
g = high-quality spectra;
b = wavelength solution appears to be wrong by more than ∼100km/s;
u = spectra have noise structure despite acceptable signal/noise.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 I1 --- P [1/6] Pointing
3- 4 I2 --- Ap [1/60] Aperture
6- 11 F6.1 km/s VHaNS [-960/1316]?=-99 Nebular emission velocity
13- 18 F6.1 km/s e_VHaNS [24/315]?=-99 Uncertainty in VHaNS
20- 25 F6.1 km/s V*c [129/1393] Corrected stellar velocity
27- 32 F6.1 km/s VLOS [-416/1354] "Observed" line-of-sight velocity
34- 39 F6.1 km/s e_VLOS [24.5/554] Uncertainty in VLOS
41- 46 F6.1 kpc r [0.3/112] Galactic radius
48- 54 F7.1 kpc e_r [0.1/2449] Uncertainty in r
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Byte-by-byte Description of file: table8.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 I1 --- P [1/6] Pointing
3- 4 I2 --- Ap [1/60] Aperture
6- 10 F5.2 --- Dn4000 [0.9/2.4] The 4000 Angstrom break
12- 16 F5.2 --- e_Dn4000 [0.01/0.1] Uncertainty in Dn4000
18- 22 F5.2 0.1nm HdA [-2.1/8] The H-delta index; Angstroms
24- 28 F5.2 0.1nm e_HdA [0.2/2.6] Uncertainty in HdA
30- 34 F5.2 0.1nm Mgb [0.03/4.3] The Mgb index; Angstroms
36- 40 F5.2 0.1nm e_Mgb [0.1/1.1] Uncerainty in Mgb
42- 46 F5.2 0.1nm <Fe> [-0.3/2.7] Composite Iron index; Angstroms
48- 52 F5.2 0.1nm e_<Fe> [0.1/0.9] Uncertainty in <Fe>
54- 58 F5.2 0.1nm [MgFe] [0.2/2.8]? The Magnesium/Iron index; Angstroms
60- 64 F5.2 0.1nm e_[MgFe] [0.1/1.8]? Uncertainty in [MgFe]
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Byte-by-byte Description of file: table9.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Fiber [1/109] Fiber number
5- 10 F6.2 arcsec oRA [-33.1/66.5] Offset distance in RA from fiber 105
12- 17 F6.2 arcsec oDE [-51.5/50] Offset distance in DEC from fiber 105
19- 22 F4.2 arcsec Diam [1.8/5.7] Fiber on-sky diameter
24- 27 F4.2 --- Ttot [0.7/0.9] Total throughput
29- 32 F4.2 --- T4 [0.5/0.9] Output flux within f/4 (1)
34- 37 F4.2 --- T4.4 [0.4/0.9] Output flux within f/4.4 (1)
39- 42 F4.2 --- T5 [0.3/0.9] Output flux within f/5 (1)
44- 47 F4.2 --- LFRD [0.04/0.3] FRD-induced throughput loss
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Note (1): Divided by input flux within f/6.3.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 30-Oct-2018