Galaxy of the Month in Hydra

• Hickson 40 in Hydra

  February 2023 - Galaxy of the Month

  After last months really rather hard challenge we have something slightly easier this month in the galaxy group Hickson 40, also known as Arp 321 and VV 116, in Hydra.

  Although this may be challenging because of its altitude from northern climes it is a really nice tight group. Consisting of three spirals, an elliptical and a lenticular galaxy this is one of the tightest groups in the Hickson catalogue. All the galaxies appear to contain compact sources, suggested to be supermassive black holes, at their centres. The size of the group is so small that all five galaxies could fit in a volume less than twice the size of our Milky Way galaxy.

  Although such compact groupings are regularly found in large galaxy clusters Hickson 40 appears to be a rather isolated field group. There actually appear to be 7 galaxies in the group but only 5 are easily seen. The group is located perhaps 300 million light-years away and is in the process of undergoing a merger to form one large elliptical galaxy. This may take place in a billion years or so.

  Hubble imaged these galaxies as part of its 32 birthday study. The group was classified by Arp as part of his class of galaxy groups.

  This group is going to be challenging for observers as none of the galaxies are bright enough to have an NGC or IC designation and the low altitude as seen from the UK, although it does crawl above the 30 degree line, will not help either.

  The brightest galaxy of the group is MCG 1-25-9 at 13.8 B so it should be visible in 30-40cm scopes from a dark sky. The rest of the group is somewhat fainter. The group is so tight that you should try using the highest power your telescope and the conditions will allow as this is also going to be the best when trying to tease out the details of the fainter members of the group.

  Unfortunately, despite being a Hickson group it does not appear in the Night Sky Observer's Guide Vol. 2. There is some information on the group on Reiner Vogel’s Hickson page.

  Owen Brazell - Galaxy Section Director

• NGC 2889 in Hydra

  March 2020 - Galaxy of the Month

  For March’s GOM we stay in in the constellation of Hydra and look at the pair of galaxies NGC 2889 and NGC 2884. William Herschel discovered NGC 2889 in 1786 but it was left to Heinrich d’Arrest to discover NGC 2884 in 1865.

  Both of these galaxies appear to be spirals but whereas NGC 2889 is seen almost face on NGC 2884 is viewed at quite an angle. The two galaxies are listed as a pair but are not currently interacting, however distance measurements would suggest that the two galaxies may be an optical pair rather than a physical pair as NGC 2889 is listed as having a distance of about 61 Mpc whereas NGC 2884 is listed with a distance of maybe 50 Mpc. They could still be a pair however if there is a sufficiently large local component to their velocities as many distance velocity calculations are dependent on the Hubble flow being the dominant component of the velocity.

  NGC 2889 was home to SN 2007rb.

  Perhaps unsurprisingly there is not much research been done on either of these galaxies and what there is mostly concentrates on generic properties of the bar in NGC 2889. Deep images also suggest that NGC 2884 is a barred spiral, however NED gives it a classification as an S0/a (a lenticular galaxy) so there appears to be some confusion over its classification.

  The two galaxies are close enough together that they will fit in the same medium (150x) to high (270x) power field of view. However given that Herschel did not see NGC 2884 it may be much fainter than NGC 2889 so a high power may be better to pick it out. Night Sky Observer's Guide (NSOG) suggests that NGC 2889 will be visible faintly in 8-10 inch scopes whilst 16-18 will show more detail and bring out NGC 2884.

  Nearby is the asterism that was given the NGC number 2879 that was also found by d’Arrest on the same night he found NGC 2884. Unfortunately it is not a true fuzzy but merely a grouping of four stars. There are a number of other very faint galaxies in this field that are likely to be beyond all but the largest telescopes visually but are probably within the range of EAA systems.

  Owen Brazell - Galaxy Section Director

• NGC 2992 in Hydra

  February 2020 - Galaxy of the Month

  The pair of galaxies that make up the major components of the group associated with NGC 2992 and NGC 2993 were first discovered by William Herschel in 1785. They were later catalogued by Arp as Arp 245 and are also in the extended VV of interacting galaxies catalogue as VV 1311. Arp added the pair to his catalogue in the group of galaxies with the appearance of fission. The group lies perhaps 100 million light-years from us. Also close by is the galaxy RFGC 1621 which may also be associated with the group, although it is not part of the interacting pair.

  The main pair are seen perhaps 100 million years after the closest point of the encounter (perigalacticon) and the interaction has already drawn out tidal tails from both galaxies. Indeed there might already be a dwarf galaxy forming in the northern tidal tail of NGC 2992.

  NGC 2992 is also a Seyfert AGN, although a fairly mild one with a classification of 1.9. It is showing some signs of revived activity, perhaps due to infall of material on to its central black hole from merger products. Radio imaging shows bubbles of material coming out at right angles from the nucleus of NGC 2992 showing a classical biconical system. There may also be small scale spiral structure in the centre which could be fuelling the accretion disk around the central black hole.

  Both NGC 2992 and NGC 2993 are connected by a faint tidal bridge as well as having their own tidal tails. RFGC 1621 appears to be a dwarf galaxy from its blue colours. Although observed with GALEX the pair do not seem to show the colours associated with new star formation. There is however a magnificent image of this pair at Adam Block's caelumobservatory website which does show new star formation in NGC 2993 as well as in the tidal tails. Both of these galaxies are catalogued as spirals, although of course they are now distorted from their encounter.

  Although not in the H400 lists NGC 2992 did make it into both Hartung’s Astronomical Objects for Southern Telescopes and Walter Scott Houston’s Deep Sky Wonders has also described the pair, although Houston does not say what size telescope was used. Night Sky Observer's Guide (NSOG) Volume 2 suggests that 12-14 inch telescopes should show the pair clearly and 20-22 inch telescopes may show the tidal tails, although I expect this is probably from a high altitude site. I am not sure if the small flat galaxy is visible given its magnitude of around 17. Given the closeness of the pair I think using a medium to high power eyepiece would be the choice for observing these. Unfortunately from the UK they never rise above the 1 airmass line so try and observe them on the meridian.

  Owen Brazell - Galaxy Section Director

  Observations

  We have an observation by Ivan Maly with his 20-inch, observing from a dark site in the Appalachian region of Pennsylvania.

• NGC 2585 in Hydra

  February 2019 - Galaxy of the Month

  In 1886, whilst observing with the 26.3” refractor at the University of Virginia’s Leander McCormick Observatory, Frank Muller came across a group of what he believed were four new nebulae.

  Unfortunately the observers at the Leander McCormick observatory were notorious for their poor reported positions for newly discovered nebulae and in this case the positions that he gave Dreyer were at least an arc-minute out.

  Based on the descriptions Muller gave however, Dreyer was able to associate three of the nebulae with a small group of galaxies which later became catalogued as NGC 2583, NGC 2584 and NGC 2585. The fourth object that Muller discovered was later determined to be a triple star, although the number NGC 2586 has sometimes been erroneously assigned to another nearby galaxy MCG -1-22-12.

  Two of the galaxies, NGC 2584 and NGC 2585 appear to form a physical pair and show signs of tidal interactions. They were given the number 1225 in the extended VV (Vorontsov-Velyaminov) catalogue of interacting galaxies. As the extended catalogue was never published in a journal (only online) the VV numbers beyond 835 are not included in the main extragalactic databases such as NED.

  There is conflicting information about whether NGC 2583 forms part of the group but its distance and redshift suggest it probably doesn’t.

  The two NGC galaxies are going to be challenging to see visually as they are at around 13-14th magnitude. If they are not challenging enough then there are two other galaxies that appear in the same field as NGC 2584/5 that have catalogue numbers from the MCG (Morphological Catalogue of Galaxies) catalogue at around 15th magnitude as MCG -1-22-6 and MCG -1-22-7.

  There are suggestions that they may also form part of a physical group with NGC 2584/5. Their redshifts are quite similar to the main pair, although the redshift of MCG-1-22-6 is perhaps a little further from that of NGC 2583. The redshift of NGC 2585 is around 6868 km/s whilst that of MCG-1-22-6 is 6590. Similar to the issues with NGC 2583 however, if the distances/redshifts associated with them are correct then it is perhaps unlikely unless the group is very widely spread in space. At a stretch MCG-1-22-12 (the galaxy erroneously assigned NGC 2586) could also be part of the group as its redshift is similar to that of NGC 2585. The group is not assigned any number in either the WBL or LGG catalogues which suggests that they at least did not see it as a physical cluster.

  The group is very small and will be challenging to find as, despite the fact it lies in the northern part of Hydra as it does not rise much above the 30 degree (one airmass) altitude line as seen from the southern UK.

  It is tight enough that all the galaxies in the main group should appear in the field of a medium power (say 250x) eyepiece. MCG-1-22-12 is slightly further away but even then it should fit in the same field as the others with a modern hyperwide eyepiece at say 200x. It may be worth using this kind of power to help darken the sky background and try and bring the galaxies out.

  NGC 2585 is a barred spiral galaxy and NGC 2584 is an Sc spiral with lots of ongoing star formation and as they both appear to be face-on spirals probably only the core will show. NGC 2583 is an elliptical galaxy. As always when observing galaxies try and find a dark site with little light pollution.

  Owen Brazell - Galaxy Section Director

• March 2017 - Galaxy of the Month

  IC 504 Group in Hydra

  Over time the Galaxy of the Month selection has varied in terms of the challenges presented from objects visible in small telescopes to ones requiring the use of the larger sized ones in amateur hands. For this month’s selection, the choice is an intriguing one in terms of how difficult they will be to see.

  The small group of galaxies around IC 504, which are IC 504, IC 505 and IC 506, were first discovered by Lewis Swift in 1888 using a 16” refractor in Rochester NY. This was perhaps not the greatest site even then. The galaxies were described by him as faint however the brighter pair should perhaps be visible in a modern 15-16” telescope.

  The galaxies are always going to be challenging ones to observe for northern observers as they lie in the head of Hydra and therefore will never rise that high, even at their best.

  These galaxies maybe physically associated and are listed in the WBL catalogue as a group of seven galaxies. The group is numbered WBL 179. I assume the other cluster members are the CGCG galaxies in the field.

  IC 504 and IC 505 are classified as lenticular galaxies in some sources and IC 506 appears to be an elliptical galaxy. Deep images from the SDSS and PanSTARRS surveys however show that IC 504 appears to have spiral arms, or at least a ring of new star formation, so perhaps it is not a lenticular but a spiral galaxy. Interestingly NED also gives the classification for IC 505 as S (spiral), which suggests some confusion, although it could of course be S0. It is also suggested that IC 505 may be a binary AGN.

  Despite being visually fainter than IC 504 it appears that IC 505 is also classified as the BCG galaxy (brightest cluster galaxy) for this group. As the SDSS image does not show any sign of spiral arms for IC 505 it appears that galaxy morphology classification is still as much as an art as much as a science.

  The field is full of much fainter galaxies when viewed on the SDSS and of particular interest is the horseshoe shaped string between IC 504 and CGCG 32-9. I doubt that any of these will be seen visually although CGCG 32-12 (MCG +1-22-7) might be with larger telescopes. There are no visual observations of this group that I have been able to find which suggests that they are well off the beaten track. Perhaps not surprisingly there is not much information on these galaxies but the suggested distance is perhaps 60 Mpc.

  For those not familiar with the PanSTARRS survey the image data is now available. Note that you cannot control the field you get and the data is not as good as the SDSS.

  Owen Brazell - Galaxy Section Director

• March 2016 - Galaxy of the Month

  NGC 2699 Galaxy Group in Hydra

  This interactive image of the NGC 2699 was provided by the Digitised Sky Survey using Aladin Sky Atlas. You can download a finder chart for the area, with another zooming in on the group of galaxies. There's a SkyTools version as well.

  This month’s choice is the group of galaxies surrounding NGC 2699 in Hydra. The Lyon catalogue (LGG) of compact galaxy clusters lists it as number 164 which consists of the galaxies NGC 2695, 2699, 2706 and 2708. Note that NGC 2706 is about 30’ away to the north from the rest of the group.

  There are a bunch of other galaxies in this field in NGC 2697, 2698 and 2709 which although in the same general area do not seem to be associated with the group as defined by the LGG selection, either that or the radial velocities have not been measured well enough.

  To add to the confusion, the UZC-GC catalogue lists the group as number 81 and it suggests the group contains the 7 galaxies NGC 2690, NGC 2695, NGC 2697, 2698, NGC 2699, NGC 2706 and NGC 2709. This is a catalogue based on automated near neighbour search techniques taking into account the recession velocities.

  The brightest two galaxies in the group NGC 2695 and 2708 were discovered by William Herschel in 1785. The rest by a ragtag list of the main NGC observers with varying size telescopes, which suggests the faintness of some of the other members.

  Deep images suggest that NGC 2708 has been undergoing some form of interaction from the tails that appear to be coming off it. This may also be why it is catalogued as an emission line galaxy, although it does not appear to have been an AGN so this maybe from some enhanced star formation.

  The majority of the group appear to be spirals with just 2699 being a confirmed elliptical. The recession velocity would put the group at a distance of around 24 Mpc.

  It is probable that NGC 2708 is the same object that John Herschel found and got added into the NGC as NGC 2727. This is another example of where different charting programs plot objects depending on whether they believe in the historical corrections or not. For more information on the dubious objects in the field see Harold Corwin’s notes on the NGC. There is also some information on these in Wolfgang’s book.

  Given the range of brightness of objects in this field I think it will be a challenge for observers. The brightest two should be visible in 22-30cm telescopes but I suspect the fainter galaxies at around 13th magnitude are going to require scopes of the order of 40cm or above to find, certainly from the kind of typical skies we have in the UK. Finding the fainter galaxies will not be helped by the fact there is a 7th magnitude star in the field.

  Owen Brazell - Galaxy Section Director

• March 2015 - Galaxy of the Month

  NGC 2713 in Hydra

  This interactive image of the NGC 2713 group was provided by the Sloan Digital Sky Survey using Aladin Sky Atlas. This finder chart should help you locate these galaxies.

  First discovered by Albert Marth in 1864 using William Lassell’s 48" Speculum metal telescope from Malta the pair of galaxies NGC 2713 and NGC 2716 will provide an interesting challenge for deep sky observers from mid northern climes. The pair was also independently rediscovered by d’Arrest in 1866.

  Residing in the head of Hydra NGC 2713 appears to form a physical pair with the nearby galaxy NGC 2716. The pair reside approximately 53 Mpc from the earth. NGC 2713 itself is a barred spiral that is highly inclined to our line of sight. NGC 2716 is a bit more difficult to classify but appears to be either an elliptical or a lenticular galaxy, recent classifications tend to the SB0 classification. NGC 2713 is classified as a radio galaxy, possibly from interactions with its companion. It may also host a weak AGN. It was also host to a type 1 supernova in 1968.

  The nearby galaxy IC 2426 may also be associated with this pair as its radial velocity is very similar, and in fact the trio is classified as a compact group number 83 in the catalogue compact groups from the UGZ. IC 2426 at 15th mag is going to be a lot more difficult to see but should fit in the same field as the others with a medium power eyepiece (say 220x)

  At about 12th magnitude NGC 2713 is not going to be easy to see but it should be visible in a 22cm telescope. NGC 2716 will be a bit more tricky but should be visible in a similar sized telescope. The pair should be visible in the same field with a medium power eyepiece.

  

  This interactive image of AGC 732 was provided by the Sloan Sky Survey.

  Owners of very large telescopes might like to see if they can see any of the components of the galaxy cluster AGC 732 just to the north of NGC 2716. The brightest galaxies here would be around 17th magnitude so I suspect they are going to be on the edge for all but the largest amateur telescopes.

  Owen Brazell - Galaxy Section Director