7 Attachment(s)
Object of the Week March 31st, 2024 – VV 124 (UGC 4879)
VV 124 / MCG +09-15-113 / CGCG 264-088 / UGC 4879
Ursa Major
Dwarf Galaxy
RA 09:16:02.0
DEC 52:50:42
Bmag +13.7
Size 2.1’ x 1.3’
Dist 4.32 million light-years
Attachment 5400
The first published image of VV 124
Our object this week is a galaxy that lies along a front leg of Ursa Major, about 2° NNW of the binocular-bright galaxy NGC 2841. It was discovered on Palomar Observatory Sky Survey (POSS) plates in the late 1950’s by Boris Vorontsov-Vel’yaminov and included as 124th entry in his 1959 Atlas and Catalogue of Interacting Galaxies [1]. His reason for doing so was because on the blue plate, several knots of 18th- and 19th-magnitude were prominent to his discerning eye. Thus, it was included under his "Galaxy Nest" category with the thinking that it was the merged remnant of two galaxies.
Attachment 5401 Attachment 5402
5' wide POSS1 Red Plate 5' wide POSS1 Blue Plate
It was next included in Vorontsov-Vel’yaminov and Arkhipova’s 1962 Morphalogical Catalogue of Galaxies (MCG) [2] and a few years later in volume three of the Catalogue of Galaxies and of Clusters of Galaxies (CGCG) [3]. In Peter Nilson’s 1973 Uppsala General Catalogue of Galaxies (UGC) [4], it received the commonly used designation UGC 4879 and the presence of “several faint very blue condensations superimposed” on the galaxy was noted. A decade later, in the first Center for Astrophysics (CfA) redshift catalogue [5], a radial velocity measurement of Vh = 600 ± 100 km s -1 was found for it. In the Hubble flow, this redshift corresponds to a distance of about 30 million light-years [6] and was copied over into the 1991 Third Reference Catalog of Bright Galaxies (RC3) [7].
In a 1985 paper by Oved Dahari [8], he classified VV 124 as a dwarf irregular galaxy. And at the turn of the century, Jansen et al [9] described the galaxy as a low-luminosity dwarf that “shows the enhanced Balmer absorption lines and blue continuum of a young ‘post-starburst’ galaxy”. Around the same time, a new radial velocity measurement of 62 ± 69 km s -1 was made in the Updated Zwicky Catalog (UZC) [10] and changed to -44 ± 69 km s -1 in the 2002 revised version of the UZC. However, these more recent measurements remained unnoted by most since the galaxy was even considered by Azzaro et al. (2006) [11] as a distant companion of NGC 2841, which lies some 46 million light-years away!
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SDSS image
In 2007, Russian astronomer A. Kopylov noted a discrepancy between the distance listed in the RC3 and the galaxy’s apparent resolution into stars on the recently released Sloan Digital Sky Survey (SDSS-I) images. This led him and his colleagues to investigate it and in 2008 released their paper titled “VV124 (UGC 4879): A New Transitional Dwarf Galaxy in the Periphery of the Local Group.” [12] Using the 6-meter Bolshoi Teleskop Azimutal’nyi (BTA) in the Caucasus Mountains, they were able to image faint enough to reach the “Tip of the Red Giant Branch” (TRGB). This showed that the galaxy was only 1.1 ± 0.1 Mpc distant…placing it about 10 times closer than previously thought! They also found that some of the knots Vorontsov-Vel’yaminov had seen are actually clumps of blue supergiants, with the brightest single star shining at magnitude +17.81 and of spectral type F5Ia. A curious finding was that the galaxy possesses some young stellar populations amongst a bulk of older, evolved stars.
Attachment 5403
Diagram from Kopylov et al (2008)
Kopylov’s findings indicated that due to its location and peculiar velocity, UGC 4879 would never have been a satellite of a major galaxy of the Local Group. Hence, it would be worth further study since it may contain a fossil record of precious information on the initial conditions of dwarf galaxies. Not surprisingly, three papers were published on the galaxy in 2011, include one using the Hubble Space Telescope. With such a telescope, Jacobs et al. [13] measured a distance of 1.36 ± 0.03 Mpc and found that nearly all of the star formation in the innermost region occurred at least 10 billion years ago. After that, star formation ceased until around 1 billion years ago. Meanwhile, using the Large Binocular Telescope, Bellazzini et al. [14] found a possible nuclear star cluster. Still in that same year, Bellazzini et al. [15] used the same HST images as Jacobs et al. to confirm their cluster candidate (C1) being a young massive one with an age of about 250 million years and a total mass around 12,000 solar masses. They were also able to identify another likely cluster (C2), significantly younger (less than 30 million years) and less massive (less than 3,500 solar masses) than C1.
In Alan McConnachie’s 2012 paper titled “The Observed Properties of Dwarf Galaxies in and Around the Local Group” [16], UGC 4879 was listed along with Leo A, the Aquarius Dwarf, and the Sagittarius Dwarf Irregular as an isolated dwarf that define the zero-velocity surface of the Local Group. And even though it had a distance of 4.44 million light-years in that work (which was less than NGC 3109 at the time), its radial velocity indicated a probable membership.
Attachment 5404
Diagram from McConnachie (2012)
Also in 2012, a group led by Evan Kirby [17] determined that it’s a “dwarf irregular far along its transformation into a dwarf spheroidal.” Not only that, but it contains dark matter in a mass-to-light ratio like dwarf spheroidals of similar stellar mass. However, they admitted that they couldn’t explain how it had somehow lost most of its gas but retained wispy, minimally rotating “wings”.
One of the most recent papers to study UGC 4879 was published in 2022 by Battaglia et al. [18]. In it, they pointed out that the two brightest stars, which had been found by Kopylov, have absolute magnitudes around -7, which is too bright even for OB stars. Thus, they suggested these might be contaminants, unresolved or partly resolved clusters.
Attachment 5406
Judy Schmidt processed HST image with clusters circled
In the middle of this month, I got a chance to attempt an observation of the LG member using my 10-inch Meade SCT. I was a bit surprised to find it visible at 91x as a soft, mildly elongated glow of fair size.
So, since its recent relocation to the edge of the Local Group, the dwarf galaxy UGC 4879 has received considerable scrutiny from professional astronomers…won’t you be next? As always…”give it a go and let us know!”
References:
[1] Vorontsov-Vel’yaminov 1959 (https://ui.adsabs.harvard.edu/abs/19......0V/abstract)
(https://ned.ipac.caltech.edu/level5/VV_Cat/frames.html)
[2] Vorontsov-Vel’yaminov & Arkhipova 1962 (https://ui.adsabs.harvard.edu/abs/19......0V/abstract)
[3] Zwicky, Herzog, & Wild 1966 (https://ui.adsabs.harvard.edu/abs/19.......Z/abstract)
[4] Nilson 1973 (https://ui.adsabs.harvard.edu/abs/19...0000N/abstract)
[5] Huchra et al. 1983 (https://ui.adsabs.harvard.edu/abs/19.....89H/abstract)
[6] Kirby et al 2012 (https://ui.adsabs.harvard.edu/abs/20.....46K/abstract)
[7] de Vaucouleurs et al. 1991 (https://ui.adsabs.harvard.edu/abs/19.......D/abstract) (https://heasarc.gsfc.nasa.gov/W3Brow...talog/rc3.html)
[8] Dahari 1985 (https://ui.adsabs.harvard.edu/abs/19....643D/abstract)
[9] Jansen et al. 2000b (https://ui.adsabs.harvard.edu/abs/2000ApJS..126..331J)
[10] Falco et al. 1999 (https://ui.adsabs.harvard.edu/abs/19....438F/abstract)
[11] Azzaro et al. 2006 (https://ui.adsabs.harvard.edu/abs/20....228A/abstract)
[12] Kopylov et al. 2008 (https://ui.adsabs.harvard.edu/abs/20.....45K/abstract)
[13] Jacobs et al 2011 (https://ui.adsabs.harvard.edu/abs/20....106J/abstract)
[14] Bellazzini et al 2011a (https://ui.adsabs.harvard.edu/abs/20.....58B/abstract)
[15] Bellazzini et al 2011b (https://ui.adsabs.harvard.edu/abs/20.....37B/abstract)
[16] McConnachie 2012 (https://ui.adsabs.harvard.edu/abs/20......4M/abstract)
[17] Kirby et al 2012 (https://ui.adsabs.harvard.edu/abs/20.....46K/abstract)
[18] Battaglia et al 2022 (https://ui.adsabs.harvard.edu/abs/20.....54B/abstract)
