Arp 187

{{short description|Radio galaxy and merger remnant}}

{{Infobox Galaxy

|name = Arp 187

| image = 250px

| caption = Arp 187 by legacy surveys. The small galaxy to the right is LEDA 980468

| credit =

|epoch = J2000

|constellation name = Eridanus

|type = Radio Galaxy {{cite web

| title=NASA/IPAC Extragalactic Database

| work=Results for Arp 187

| url=http://ned.ipac.caltech.edu/cgi-bin/objsearch?objname=arp+187

| accessdate=2006-10-26 }}

|appmag_v = 15.3

|size_v = 0.8 x 0.6

|z = 12095 ± 45 km/s

|ra = {{RA|5|03|53}}

|dec = {{DEC|-10|14|51}}

|names = PGC 16691

}}

Arp 187 is a radio galaxy and merger remnant located in the constellation Eridanus. It is an interacting galaxy pair (MCG-02-13-040).{{cite web|url=http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=arp+187+&submit=SIMBAD+search |title=Simbad |accessdate=2010-01-06}} It is included in the Atlas of Peculiar Galaxies in the category galaxies with narrow filaments.

The galaxy has two prominent radio lobes, however the emission of its AGN in X-ray is low, and so is the thermal output of the AGN torus as observed in infrared, suggesting that it has been quenched. The detection of a narrow line region (with dimensions up to 10 kpc) with still active emission mean that the AGN was still active up to at least 10^4-5 years ago. In the nucleus of Arp 187 is predicted to lie a supermassive black hole (SMBH) with estimated mass around 6.7 × 10⁸ {{solar mass|link=yes}}.{{cite journal |last1=Ichikawa |first1=Kohei |last2=Ueda |first2=Junko |last3=Shidatsu |first3=Megumi |last4=Kawamuro |first4=Taiki |last5=Matsuoka |first5=Kenta |title=Signs of active galactic nucleus quenching in a merger remnant with radio jets |journal=Publications of the Astronomical Society of Japan |date=1 February 2016 |volume=68 |issue=1 |pages=9 |doi=10.1093/pasj/psv112|arxiv=1510.06037 }} Further observations of such a SMBH with a quenched AGN were published in 2019.{{cite web |url=https://www.sci.tohoku.ac.jp/english/news/20190401-10200.html |title=Active Galactic Nucleus caught in the act of "dying" 〜light echo delivers the information before the death〜

|date=1 April 2019 |website=Tohoku university}}{{cite journal |vauthors=Ichikawa K, Ueda J, Bae H et al|date=9 January 2019 |title=Discovery of Dying Active Galactic Nucleus in Arp 187: Experience of Drastic Luminosity Decline within 104 yr |journal=The Astrophysical Journal|volume=870 |issue=2 |page=65 |doi=10.3847/1538-4357/aaf233|arxiv=1811.07447|bibcode=2019ApJ...870...65I |s2cid=119466692 |doi-access=free }}{{cite web |url=https://www.tohoku.ac.jp/en/press/discovery_of_dying_supermassive_black_hole.html|title=Discovery of a Dying Supermassive Black Hole Via a 3000-year-long Light Echo|date=4 June 2021 |website=Tohoku university}}