Page last updated Oct 9, 2017|
PGC 17109 (with J0519403+034354 = Arp 52)
A magnitude 15(?) spiral galaxy (type SAB(rs)bc? pec) in Orion (RA 05 19 40.6, Dec +03 43 47)
and a magnitude ?? lenticular galaxy (type E/S0?) at RA 05 19 40.3, Dec +03 43 54
Physical Information: Arp 52 consists of PGC 17109, and the small companion near its northwestern rim. It is used by the Arp Atlas as an example of a spiral galaxy with a small high surface brightness companion. Based on a recessional velocity of 8375 km/sec (and H0 = 70 km/sec/Mpc), a straightforward calculation indicates that PGC 17109 is about 390 million light years away. However, for objects at such distances we should take into account the expansion of the Universe during the time it took their light to reach us. Doing that shows that the galaxy was about 375 to 380 million light years away at the time the light by which we see it was emitted, about 380 to 385 million years ago (the difference between the two numbers being due to the expansion of the intervening space during the light-travel time). Given that and its apparent size of about 0.8 by 0.45 arcmin (from the images below), PGC 17109 is about 85 to 90 thousand light years across. If its apparent companion is a real companion (and therefore at the same distance), as appears to be the case (based on the somewhat distorted appearance of the larger galaxy), its apparent size of about 0.065 by 0.04 arcmin (also from the images below) would correspond to about 7 thousand light years. I have not been able to find anything about the smaller galaxy, even its designation (if any exists), hence my naming it according to its position.
Above, a SDSS image overlaid on a 12 arcmin wide DSS image centered on PGC 17109
Below, a 1 arcmin wide SDSS image of the apparent galaxy pair
A magnitude 14(?) irregular galaxy (type dIrr?) in Lepus (RA 05 27 05.8, Dec -20 40 40)
Designation Note: Recognized by its PGC designation in LEDA and NED, but the news release associated with the HST image below uses the designation ESO553-046.
Physical Information: Based on a recessional velocity of 545 km/sec (and H0 = 70 km/sec/Mpc), PGC 17302 is about 25 million light years away, in good agreement with a single redshift-independent distance estimate of about 20 to 25 million light years. Given that and its apparent size of about 0.95 by 0.75 arcmin (from the HST image below), the galaxy is only about 7 thousand light years across. The galaxy has one of the highest rates of star formation in the thousand galaxies closest to our Milky Way galaxy, and is classified as a Blue Compact Dwarf (BCD) because of the large number of hot blue-white stars in the numerous clusters scattered throughout the southern portion of the galaxy (reddish structures represent hydrogen gas heated by the radiation from those stars). Like many such galaxies it lacks a nucleus, and is almost devoid of elements heavier than helium, indicating that the supernovae that must end the lives of its hot young stars have not yet had time to significantly change the composition of its interstellar material from the primordial composition of the very early Universe.
Above, a 12 arcmin wide DSS image centered on PGC 17302
(The glare on the left side of the image is from the magnitude 2.8 star β Leporis)
Below, a 1 arcmin wide DSS image of the galaxy
Below, a 1 arcmin wide PanSTARRS image of the galaxy
Below, a 1.2 by 1.5 arcmin wide HST image of the galaxy (Image Credit ESA/Hubble & NASA)