The Calibration and Data Products of GALEX

Abstract

We describe the calibration status and data products pertaining to the GR2 and GR3 data releases of the Galaxy Evolution Explorer (GALEX ). These releases have identical pipeline calibrations that are significantly improved over the GR1 data release. GALEX continues to survey the sky in the far-ultraviolet (FUV, $154 nm) and near-ultraviolet (NUV, $232 nm) bands, providing simultaneous imaging with a pair of photon-counting, microchannel plate, delay line readout detectors. These 1.25 field of view detectors are well suited to ultraviolet observations because of their excellent red rejection and negligible background. A dithered mode of observing and photon list output pose complex requirements on the data processing pipeline, entangling detector calibrations, and aspect reconstruction algorithms. Recent improvements have achieved photometric repeatability of 0.05 and 0.03 m AB in the FUV and NUV, respectively. We have detected a long-term drift of order 1% FUV and 6% NUVover the mission. Astrometric precision is of order 0.5 00 rms in both bands. In this paper we provide the GALEX user with a broad overview of the calibration issues likely to be confronted in the current release. Improvements are likely as the GALEX mission continues into an extended phase with a healthy instrument, no consumables, and increased opportunities for guest investigations.

A Catalog of Galex Ultraviolet Emission From Spectroscopically Confirmed M Dwarfs*

“…The data contain images in a near-UV band from ∼1750 to 2750 Å and a far-UV band from ∼1350 to 1750 Å. More information about the GALEX data releases can be found in Martin et al (2005) and Morrissey et al (2007) as well as at the GALEX website, part of the Mikulski Archive for Space Telescopes (MAST). 4…”

THE 31 DEG2 RELEASE OF THE STRIPE 82 X-RAY SURVEY: THE POINT SOURCE CATALOG

“…We searched for counterparts to the XMM-Newton AO13 sources in publicly available multi-wavelength databases: SDSS, WISE (Wright et al 2010), UKIDSS (Hewett et al 2006;Casali et al 2007;Lawrence et al 2007), VHS (McMahon et al 2013), GALEX (Morrissey et al 2007), FIRST, and the Herschel Survey of Stripe 82 (HerS; Viero et al 2014). To determine whether a multi-wavelength association to an X-ray source represents the true astrophysical counterpart rather than a chance coincidence, we use the maximum likelihood estimator method (MLE; Sutherland & Saunders 1992) to match between the X-ray source lists and the ancillary catalogs.…”

“…This catalog represents data from the mediumimaging survey (MIS) in GALEX Release 7 (Morrissey et al 2007). With a R crit value of 0.75 for both bands, we find 572 and 407 counterparts, with 12 and 5 spurious associations, in the NUV and FUV bands, respectively (see Figure 8).…”

“…The coadded photometry reaches 1.2-2.2 magnitudes deeper than any single SDSS scan (r∼24.6 versus r∼22.2; Annis et al 2014;Jiang et al 2014), and the full field has existing optical spectroscopy from SDSS and SDSS BOSS (Data Releases 9 and 10; Ahn et al 2012Ahn et al , 2014, 2 SLAQ (Croom et al 2009), and WiggleZ (Drinkwater et al 2010), with partial coverage from DEEP2 (Newman et al 2013), PRIMUS (Coil et al 2011), 6dF (Jones et al 2004(Jones et al , 2009, the VIMOS VLT Deep Survey (VVDS Garilli et al 2008), a deep spectroscopic survey of faint quasars from Jiang et al (2006), and a pre-BOSS pilot survey using Hectospec on MMT (Ross et al 2012). Existing multi-wavelength data in Stripe 82 include near-infrared observations from UKIDSS (Hewett et al 2006;Casali et al 2007; Lawrence et al 2007) and the VISTA Hemisphere Survey (VHS; McMahon et al 2013); farinfrared coverage from Herschel over 79 deg 2 (Viero et al 2014); ultraviolet coverage with GALEX (Morrissey et al 2007); radio observations at 1.4 GHz with Faint Images of the Radio Sky at Twenty centimeters (FIRST) (Becker et al 1995;White et al 1997;Becker et al 2012;Helfand et al 2015), with deeper VLA coverage over 80 deg 2 (Hodge et al 2011); and millimeter observations with the Atacama Cosmology Telescope (ACT; Fowler et al 2007;Swetz et al 2011). Additionally, there is Spitzer coverage in the field from the Spitzer-HETDEX Exploratory Large Area survey over 28 deg 2 (SHELA; PI: C. Papovich) and the Spitzer IRAC Equatorial Survey over 110 deg 2 (SpIES; PI: G. Richards; J.…”

Star-forming compact groups (SFCGs): an ultraviolet search for a local sample

“…there is significant overlapping. We identify duplicate objects by cross-matching the GALEX sample with itself, using a 6 arcsec search radius, slightly larger than 4.2 and 5.3 arcsec angular resolution of the GALEX FUV and NUV images, respectively (Morrissey et al 2007). …”