GALEX Early Release Data

5. Quick Look (Basic) Imaging File Description.

6. Quick Look (Basic) Spectroscopy File Description.

1. Overview

The early data release contains images and catalogs generated by the GALEX data pipeline in Nov-Dec 2003. These data products are representative of what will be provided to Guest Investigators and to the astronomical community in the first major public data release (DR1) in Fall 2004. This document describes the release data and provides additional information regarding data collection modes, performance parameters and pipeline performance.

2. Early Release Description

The GALEX surveys are on-going. At the start of December 2003, GALEX has already observed over 3000 square degrees of sky during more than 2000 orbits. For the all-sky and medium imaging surveys, the early release observations contain less than 1% of what has been collected to date, with the single DIS/WSS field one of 10-15 deep fields that has been observed.

Figure 1.1 below shows the location of the ERO targets. The ERO fields and exposure times were selected to provide a representative data set for use by prospective investigators. Targets observed at different Galactic latitudes with varying infrared cirrus levels (100 mm) have a wide range of extinction values and UV background levels The median cirrus level over the whole sky is ~ 3.0 MJy/sr. GALEX deep imaging and spectroscopy fields are generally selected to have I₁₀₀ < 1.0 MJy/sr. Currently the All-sky survey is limited to fields with cirrus levels below 3.0 MJy/sr.

Figure 1 .1 (a) Aitoff projection of SFD dust maps (Galactic coordinates) w/ ERO target locations indicated. (b) Cumulative distribution of cirrus and levels for ERO targets.

Survey	TARGET	RA	DEC	GLON	GLAT	I₁₀₀	E(B-V)	EXP	COMMENTS
AIS	AISCHV2_275_30470_0001_sv06	12.89	-27.23	290	-89.8	0.75	0.015	109	High Galactic Latitude
AIS	AISCHV2_160_19659_0001_sv01	312.83	8.71	55.7	-22	4.2	0.080	115	Low Galactic Latitude
AIS	AISCHV2_153_29114_0002_sv10	347.56	-0.20	76.7	-54	2.3	0.049	113	Overlaps SDSS DR1
AIS	AISCHV2_153_29114_0002_sv11	346.98	0.67	76.9	-53	2.1	0.049	111	Overlaps SDSS DR1
AIS	AISCHV2_153_29114_0002_sv12	346.50	-0.11	75.4	-53	2.6	0.055	113	Overlaps SDSS DR1
AIS	AISGRID_359_33627_0001_sv03	219.68	5.31	357.2	56.4	1.8	0.035	238	NGC 5701 gorgeous ring-bar liner
MIS	MISDR1_29116_0381_0001	347.56	-0.20	76.69	-54	2.3	0.049	1492	Overlaps SDSS DR1
NGS	NGS_M51	201.90	47.07	104.9	68.5	1.4	0.022	1412	The Whirlpool Galaxy
DIS	ELAISS1_00	9.64	-43.99	-72	-43	0.5	0.007	12198	~1/3 planned DIS depth
WSS	ELAISS1_00	9.64	-43.99	-72	-43	0.5	0.007	31267	DIS used for detection image

3. Early Release Download Data

The ERO release includes two categories of release files. A "basic" set provides the user with a minimal source extraction catalog and images which can be used for an initial "quick look". We also provide an "advanced" set which contains the full complement of pipeline outputs for each of these observations. Many of these outputs are beyond the scope of this document and will be described in more detail elsewhere. Nevertheless, many users---particularly potential Guest Investigators---may find it useful to explore the full set of pipeline outputs.

For a single imaging target, six files are available for download:

1. Imaging Basic Data Set

a. gzipped tar file (containing the two image and two catalog files listed below)

b. FUV intensity image [fits]

c. NUV intensity image [fits]

d. Basic matched catalog [fits]

e. Basic matched catalog [text]

2. Imaging Full Data Set

a. gzipped tar file (contains the full pipeline output directory)

For a single spectroscopy target, two files are available for download:

3. Spectroscopy Basic Data Set

a. 1-D Combined Spectra [fits]

4. Spectroscopy Full Data Set

a. gzipped tar file (contains the full pipeline output directory)

All of these files may be downloaded by using the available links. The gzipped tar files for the full pipeline directories may be quite large (several hundred GB).

4. Filenaming Convention

A filename contains a basename (or prefix), a suffix and an extension. (e.g. AISCHV2_153_29114_0002_sv11-xd-mcat.fits)

The filename basename contains alphanumeric characters (of unspecified length, but containing no hyphens or periods, e.g. "AISCHV2_153_29114_0002_sv11" above). Typically this basename is related to the observed target. Files in directories containing multi-leg observations (e.g. all-sky survey) will have "_sv##" appended to the prefix with ## indicating the number of the sub-visit of that particular leg. No other requirements have been placed on the filename prefix.

The filename suffix contains delimited file type descriptor strings. Table XX shows the full set of files currently being generated by orbpipe. The rows in bold indicate those files that will be most useful for a first look at the GALEX data. The filename suffix may begin with a band/mode substring:

-nd- NUV direct (imaging)

-fd- FUV direct (imaging)

-xd- Merged direct (imaging)

-ng- NUV grism

-fg- FUV grism

-xg- Merged grism

-no- NUV opaque

-fo- FUV opaque

Pipeline files which are generated for both NUV and FUV are indicated with "[n or f]" in the pipeline products table.

5. Quick Look (Basic) Imaging File Description

-[f,n]d-int.fits:

fits images from fuv [f] or nuv [n] channel in the imaging (direct d) mode. Images are intensity maps [int] which are created from count [cnt] images [in detected counts=photons], divided by exposure [exp] images [in seconds]. Images are 3840 by 3840 pixels, pixels are 1.5"x1.5" arcseconds. 1 count in a pixel corresponds roughly to a flat-fielded 1 ct/s. These images are not background subtracted. Image is in pixels with J2000 world coordinate system (WCS). Image can be immediately viewed in sky coordinates using ds9, gaia, or other image viewing routines.

-mcat_basic.fits:

reduced fits binary table of matched (FUV+NUV) sources detected from a single image.

-mcat_basic.txt:

text table of matched (FUV+NUV) sources with key subset of source attributes available in full .fits table.

Table 1.2 -- Extracted columns in text matched catalog:

Parameter	Units	Format	Content
RA_J2000, DEC_J2000	Degrees [decimal]		J2000 RA & DEC of matched source position
mag_FUV	AB magnitude		Calibrated FUV magnitude
mag_err_FUV	AB magnitude		Calibrated FUV magnitude error
mag_NUV	AB magnitude		Calibrated NUV magnitude
mag_err_NUV	AB magnitude		Calibrated NUV magnitude error
F_FUV	mJy		Calibrated FUV flux
F_err_FUV	mJy		Calibrated FUV flux error
F_NUV	mJy		Calibrated NUV flux
F_err_NUV	mJy		Calibrated NUV flux error
Artifact FLAG	Bit		Artifact flags
2^nd moment FUV	Arcsec		Rms object size
2^nd moment NUV	Arcsec		Rms object size
E(B-V)	Mag		Galactic reddening obtained from Schlegel, REF.

6. Quick Look (Basic) Spectroscopy File Description

-xg-gsp.fits file

The xg-gsp.fits file is the final product from the spectroscopy pipeline. From the spectral image strip files (-?g-pri.fits), uncalibrated spectra are extracted and stored in extracted spectra files (-[n,f]g-xsp.fits). These files are then combined to create the *-xg-gsp.fits file which contains the band-combined flux-calibrated extracted spectra data, in units of photons per second per centimeter squared per Angstrom vs. Angstrom, on a linear dispersion scale. The range is roughly

1300 to 3000 Angstroms. The two bands are joined at approximately 1800 Angstroms with no overlapping region.

After a combined strip is built up from individual grism rotation image strips, a final merged, flux calibrated spectrum is extracted and stored in the xg-gsp.fits file. In this example from the ELAISS1_00 WSS data, GALEX has detected a known quasar and also an X-ray source (Alexander et al (2001) object #11) at z=0.398. OVI, Lyman Alpha, C IV, CIII lines are seen at measured wavelengths (1445, 1700, 2165 and 2660 respectively).

The following table contains a description of the xg-gsp file columns.

Parameter	Col #	Format	Description
ggoid	1	(2J)	Global ID of spectral source
ggoid_D	2	(2J)	Global ID of direct image source
band	3	(1J)	1=nuv only, 2=fuv only, 3=both
id	4	(1J)	Spectral source ID { corresponds to direct image catalog ID }
alpha_j2000	5	(1D)	Right Ascension J2000 (deg)
delta_j2000	6	(1D)	Declination J2000 (deg)
numpt	7	(1J)	Number of points in spectra
truthid	8	(1J)	Truth catalog ID (matched) { used only for simulations, not real data }
objtype	9	(1J)	Object Type(0=galaxy,1=star) { a guess based on FUV - NUV color. }
temperature	10	(1E)	Estimated effective temper.(K)
redshift	11	(1E)	Estimated redshift { not used yet }
slope	12	(1E)	Estimated spectral slope
weight	13	(2E)	Average weight (each band) { effective exposure (response) }
background	14	(2E)	Average background (each band)
median_s2n	15	(2E)	Median Signal/Noise (each band)
centroid	16	(2E)	Relative position(spatial)(each) { spatial centroid on spectral image strip }
specfwhm	17	(2E)	Estim. Spatial FWHM (each band) { arcseconds }
nuv_numpro	18	(1J)	Number of points in NUV profile
fuv_numpro	19	(1J)	Number of points in FUV profile
nuv_profile	20	(79E)	NUV profile (spatial)
fuv_profile	21	(79E)	FUV profile (spatial) { spatial profile using a high response region of spectral image strip }
nuv	22	(1E)	Direct image flux rate (NUV)
nuve	23	(1E)	Error in direct image flux rate
fuv	24	(1E)	Direct image flux rate (FUV)
fuve	25	(1E)	Error in direct image flux rate
nuvs	26	(1E)	Spectral flux scaled to direct
nuvse	27	(1E)	Error in nuvs
fuvs	28	(1E)	Spectral flux scaled to direct
fuvse	29	(1E)	Error in fuvs { columns 26-29 use the extrapolations for wings of response functions }
nuv0s	30	(1E)	NUV Zeroth order flux rate
nuv0se	31	(1E)	label for field 31
nuv1s	32	(1E)	NUV First order flux rate
nuv1se	33	(1E)	label for field 33
nuv2s	34	(1E)	NUV Second order flux rate
nuv2se	35	(1E)	label for field 35
fuv1s	36	(1E)	FUV First order flux rate
fuv1se	37	(1E)	label for field 37
fuv2s	38	(1E)	FUV Second order flux rate
fuv2se	39	(1E)	label for field 39
fuv3s	40	(1E)	FUV Third order flux rate
fuv3se	41	(1E)	label for field 41 { columns 30-41 use selected high response regions }
zero	42	(1E)	Wavelength of first pixel (Ang.)
disp	43	(1E)	Angstroms per pixel { The zero and disp values set the linear wavelength scale
obj	44	(488E)	Flux (pho/sec/cm^2/Ang) (standard)
objerr	45	(488E)	Error on obj { Calibrated spectral data. This extraction is a simple summation of the object region after subtracting off the average background at each spectral point. }
opx	46	(488E)	Flux (pho/sec/cm^2/Ang) (optimal)
opxerr	47	(488E)	Error on opx { Optimal extraction arrays not used yet. }