J/A+A/530/A86 Hubble Legacy Archive ACS grism data (Kuemmel+, 2011)
The Hubble Legacy Archive ACS grism data.
Kuemmel M., Rosati P., Fosbury R., Haase J., Hook R.N., Kuntschner H.,
Lombardi M., Micol A., Nilsson K.K., Stoehr F., Walsh J.R.
<Astron. Astrophys., 530, A86 (2011)>
=2011A&A...530A..86K 2011A&A...530A..86K
ADC_Keywords: Surveys ; Spectroscopy
Keywords: methods: data analysis - space vehicles: instruments -
techniques: imaging spectroscopy - surveys
Abstract:
A public release of slitless spectra, obtained with ACS/WFC and the
G800L grism, is presented. Spectra were automatically extracted in a
uniform way from 153 archival fields (or "associations")
distributed across the two Galactic caps, covering all observations to
2008. The ACS G800L grism provides a wavelength range of 0.55-1.00um,
with a dispersion of 40Å/pixel and a resolution of ∼80Å for
point-like sources. The ACS G800L images and matched direct images
were reduced with an automatic pipeline that handles all steps from
archive retrieval, alignment and astrometric calibration, direct image
combination, catalogue generation, spectral extraction and collection
of metadata. The large number of extracted spectra (73,581) demanded
automatic methods for quality control and an automated classification
algorithm was trained on the visual inspection of several thousand
spectra. The final sample of quality controlled spectra includes 47919
datasets (65% of the total number of extracted spectra) for 32149
unique objects, with a median iAB-band magnitude of 23.7, reaching
26.5 AB for the faintest objects. Each released dataset contains
science-ready 1D and 2D spectra, as well as multi-band image cutouts
of corresponding sources and a useful preview page summarising the
direct and slitless data, astrometric and photometric parameters. This
release is part of the continuing effort to enhance the content of the
Hubble Legacy Archive (HLA) with highly processed data products which
significantly facilitate the scientific exploitation of the Hubble
data. In order to characterize the slitless spectra, emission-line
flux and equivalent width sensitivity of the ACS data were compared
with public ground-based spectra in the GOODS-South field. An example
list of emission line galaxies with two or more identified lines is
also included, covering the redshift range 0.2-4.6. Almost all
redshift determinations outside of the GOODS fields are new. The scope
of science projects possible with the ACS slitless release data is
large, from studies of Galactic stars to searches for high redshift
galaxies.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 38 15 List of failed associations
tablea2.dat 96 54 Objects with determined redshifts
tablea3.dat 112 440 The associations included in this release
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Association (field) designation
11- 12 I2 h RAh Right ascension (J2000)
14- 15 I2 min RAm Right ascension (J2000)
17- 21 F5.2 s RAs Right ascension (J2000)
23 A1 --- DE- Declination sign (J2000)
24- 25 I2 deg DEd Declination (J2000)
27- 28 I2 arcmin DEm Declination (J2000)
30- 33 F4.1 arcsec DEs Declination (J2000)
35- 36 I2 --- Ngrism Number of grism datasets
38 I1 --- Note [1/4] Reasons of exclusion (1)
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Note (1): Code for exclusion as follows:
1 = Insufficient direct images
2 = object density too high
3 = not sufficient grism images
4 = bad background subtraction for grism images
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- --- [HAG_]
5- 33 A29 --- HLA Hubble Legacy Archive object designation
(JHHMMSS.ss+DDMMSS.s_AAAAAAAAA) (1)
35- 43 F9.5 deg RAdeg Right ascension in decimal degrees (J2000)
45- 53 F9.5 deg DEdeg Declination in decimal degrees (J2000)
55- 59 F5.3 --- z ?=- Redshift
60 A1 --- n_z [a-d] Discrepancies on z (2)
62- 66 F5.3 --- e_z ?=- rms uncertainty on z
68- 96 A29 --- Lines Line identifications
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Note (1): where AAAAAAAAA is the association name.
HAG JHHMMSS.ss+DDMMSS.s in Simbad.
Note (2): Notes on redshift as follows:
a = Redshift undetermined from our spectrum, redshift in table from
Wirth et al. (2004, Cat. J/AJ/127/3121)
b = Barger et al. (2002AJ....124.1839B 2002AJ....124.1839B) reports a redshift of z=2.922
for this source, but the our slitless spectrum appears to be of
better quality and we retain our redshift determination.
c = Redshift from our grism spectrum is zgr=0.718±0.003, but the
redshift given in the table comes from a better quality spectrum
of Wirth et al. (2004, Cat. J/AJ/127/3121).
d = For this source, Barger et al. (2008, Cat. J/ApJ/689/687) reports
a redshift of z=0.247. As this spectrum is not available for
inspection, and the our spectrum is of good quality, we retain
the redshift determined from our grism spectrum.
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Byte-by-byte Description of file: tablea3.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Association designation
11- 12 I2 h RAh Right ascension (J2000)
14- 15 I2 min RAm Right ascension (J2000)
17- 21 F5.2 s RAs Right ascension (J2000)
23 A1 --- DE- Declination sign (J2000)
24- 25 I2 deg DEd Declination (J2000)
27- 28 I2 arcmin DEm Declination (J2000)
30- 33 F4.1 arcsec DEs Declination (J2000)
35- 45 F11.7 deg GLON Galactic longitude
47- 57 F11.7 deg GLAT Galactic latitude
60- 65 F6.1 deg Orient Orientation of the y-axis in the
detection image
67- 76 A10 "YYYY-MM-DD" Date Observation date
78- 83 A6 --- Filt HST filter name
85- 86 I2 --- Nimg Number of images
88- 94 F7.1 s Timg Exposure time for image
96- 97 I2 --- Ngr ? Number of grism datasets
99-105 F7.1 s Tgr ? Exposure time for grism
107-110 I4 --- Nobj ? Number of objects
112 I1 --- Qual [0/2]? Image quality of detection image:
0=very good, 1=acceptable, 2=not optimal.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 15-Sep-2011