The NASA/IPAC Extragalactic Database (NED) has deployed a new rule-based cross-matching algorithm called Match Expert (MatchEx), capable of cross-matching very large catalogs (VLCs) with >10 million objects. MatchEx goes beyond traditional position-b
ased cross-matching algorithms by using other available data together with expert logic to determine which candidate match is the best. Furthermore, the local background density of sources is used to determine and minimize the false-positive match rate and to estimate match completeness. The logical outcome and statistical probability of each match decision is stored in the database, and may be used to tune the algorithm and adjust match parameter thresholds. For our first production run, we cross-matched the GALEX All Sky Survey Catalog (GASC), containing nearly 40 million NUV-detected sources, against a directory of 180 million objects in NED. Candidate matches were identified for each GASC source within a 7.5 arcsecond radius. These candidates were filtered on position-based matching probability, and on other criteria including object type and object name. We estimate a match completeness of 97.6% and a match accuracy of 99.75%. MatchEx is being used to cross-match over 2 billion catalog sources to NED, including the Spitzer Source List, the 2MASS Point-Source Catalog, AllWISE, and SDSS DR 10. It will also speed up routine cross-matching of sources as part of the NED literature pipeline.
We present a Spitzer Infrared Spectrograph (IRS) map of H2 emission from the nearby galaxy NGC 4258 (Messier 106). The H2 emission comes from 9.4E6 Msun of warm molecular hydrogen heated to 240-1040 K in the inner anomalous arms, a signature of jet i
nteraction with the galaxy disk. The spectrum is that of a molecular hydrogen emission galaxy (MOHEG), with a large ratio of H2 over 7.7 micron PAH emission (0.37), characteristic of shocked molecular gas. We find close spatial correspondence between the H2 and CO emission from the anomalous arms. Our estimate of cold molecular gas mass based on CO emission is 10 times greater than our estimate of 1.0E8 Msun based on dust emission. We suggest that the X(CO) value is 10 times lower than the Milky Way value because of high kinetic temperature and enhanced turbulence. The H2 disk has been overrun and is being shocked by the jet cocoon, and much of the gas originally in the disk has been ejected into the galaxy halo in an X-ray-hot outflow. We measure a modest star formation rate of 0.08 Msun/yr in the central 3.4 square kpc that is consistent with the remaining gas surface density.
The Spitzer spectrum of the giant FR II radio galaxy 3C 326 is dominated by very strong molecular hydrogen emission lines on a faint IR continuum. The H2 emission originates in the northern component of a double-galaxy system associated with 3C 326.
The integrated luminosity in H2 pure-rotational lines is 8.0E41 erg/s, which corresponds to 17% of the 8-70 micron luminosity of the galaxy. A wide range of temperatures (125-1000 K) is measured from the H2 0-0 S(0)-S(7) transitions, leading to a warm H2 mass of 1.1E9 Msun. Low-excitation ionic forbidden emission lines are consistent with an optical LINER classification for the active nucleus, which is not luminous enough to power the observed H2 emission. The H2 could be shock-heated by the radio jets, but there is no direct indication of this. More likely, the H2 is shock-heated in a tidal accretion flow induced by interaction with the southern companion galaxy. The latter scenario is supported by an irregular morphology, tidal bridge, and possible tidal tail imaged with IRAC at 3-9 micron. Unlike ULIRGs, which in some cases exhibit H2 line luminosities of comparable strength, 3C 326 shows little star-formation activity (~0.1 Msun/yr). This may represent an important stage in galaxy evolution. Starburst activity and efficient accretion onto the central supermassive black hole may be delayed until the shock-heated H2 can kinematically settle and cool
