Triangulum II

{{Short description|Galaxy in the constellation Triangulum}}

{{sky|02|13|17.4|+|36|10|42.4|98000}}

{{ Infobox Galaxy

| image =

| caption =

| name = Triangulum II

| epoch = J2000

| type =

| ra = {{RA|02|13|17.4}}

| dec = +{{DEC|36|10|42.4}}

| dist_ly = {{convert|30|+/-|2|kpc|kly|abbr=on|lk=on|disp=flip}}

| z =

| mass_light_ratio = 3600 (V)

| appmag_v =

| size_v = 3.9′

| age= 13 Ga

| constellation name = Triangulum

| names = Triangulum II, Tri II, Laevens 2, Lae 2

}}

Triangulum II (Tri II or Laevens 2) is a dwarf galaxy close to the Milky Way Galaxy. Like other dwarf spheroidal galaxies, its stellar population is very old: the galaxy was quenched before 11.5 billion years ago.{{cite journal|doi=10.3847/2041-8213/ac2aa3|title=Star Formation Histories of Ultra-faint Dwarf Galaxies: Environmental Differences between Magellanic and Non-Magellanic Satellites?|year=2021|last1=Sacchi|first1=Elena|last2=Richstein|first2=Hannah|last3=Kallivayalil|first3=Nitya|last4=Van Der Marel|first4=Roeland|last5=Libralato|first5=Mattia|last6=Zivick|first6=Paul|last7=Besla|first7=Gurtina|last8=Brown|first8=Thomas M.|last9=Choi|first9=Yumi|last10=Deason|first10=Alis|last11=Fritz|first11=Tobias|last12=Geha|first12=Marla|author12-link= Marla Geha |last13=Guhathakurta|first13=Puragra|last14=Jeon|first14=Myoungwon|last15=Kirby|first15=Evan|last16=Majewski|first16=Steven R.|last17=Patel|first17=Ekta|last18=Simon|first18=Joshua D.|last19=Tony Sohn|first19=Sangmo|last20=Tollerud|first20=Erik|last21=Wetzel|first21=Andrew|journal=The Astrophysical Journal Letters|volume=920|issue=1|pages=L19|arxiv=2108.04271|bibcode=2021ApJ...920L..19S|s2cid=236965965 |doi-access=free }} It contains only 1000 stars, yet is quite massive, having a solar mass to light ratio of 3600. This is an unusually high mass for such a small galaxy.

{{cite web

|last1=Dajose|first1=Lori |title= Dark matter dominates in nearby dwarf galaxy |url= http://phys.org/news/2015-11-dark-dominates-nearby-dwarf-galaxy.html |accessdate= 19 November 2015 |date= 18 November 2015 |publisher= Phys.org

}}; {{cite web| publisher=Caltech | title=Dark Matter Dominates in Nearby Dwarf Galaxy | author=Lori Dajose | date=November 18, 2015 | access-date=December 16, 2015 | url=http://www.caltech.edu/news/dark-matter-dominates-nearby-dwarf-galaxy-48790}}

The distance from the centre of the Milky Way is {{convert|26|kpc|kly|abbr=on}}. The luminosity is 450 times that of the Sun.

{{cite journal

|last1=Kirby|first1=Evan N.|last2=Cohen|first2=Judith G.|author-link2=Judith Gamora Cohen|last3=Simon|first3=Joshua D.|last4=Guhathakurta|first4=Puragra

|title= Triangulum II: Possibly a Very Dense Ultra-Faint Dwarf Galaxy |journal= The Astrophysical Journal |date= 16 November 2015 |volume= 814 |issue= 1 |pages= L7 |doi= 10.1088/2041-8205/814/1/L7 |bibcode= 2015ApJ...814L...7K |arxiv= 1510.03856

|s2cid=13600560 }}

This makes it one of the dimmest known galaxies. The 2D half light radius is {{convert|34|pc|ly|abbr=on}}. The galaxy was discovered in images taken by Pan-STARRS by Benjamin P. M. Laevens in 2015.

{{cite journal

|last1=Laevens|first1=Benjamin P. M.|last2=Martin|first2=Nicolas F.|last3=Ibata|first3=Rodrigo A.|last4=Rix|first4=Hans-Walter|last5=Bernard|first5=Edouard J.|last6=Bell|first6=Eric F.|last7=Sesar|first7=Branimir|last8=Ferguson|first8=Annette M. N.|last9=Schlafly|first9=Edward F.|last10=Slater|first10=Colin T.|last11=Burgett|first11=William S.|last12=Chambers|first12=Kenneth C.|last13=Flewelling|first13=Heather|last14=Hodapp|first14=Klaus A.|last15=Kaiser|first15=Nicholas|last16=Kudritzki|first16=Rolf-Peter|last17=Lupton|first17=Robert H.|last18=Magnier|first18=Eugene A.|last19=Metcalfe|first19=Nigel|last20=Morgan|first20=Jeffrey S.|last21=Price|first21=Paul A.|last22=Tonry|first22=John L.|last23=Wainscoat|first23=Richard J.|last24=Waters|first24=Christopher|display-authors=10

|title= A New Faint Milky Way Satellite Discovered in the PAN-STARRS1 3π Survey |journal= The Astrophysical Journal |date= 31 March 2015 |volume= 802 |issue= 2 |pages= L18 |doi= 10.1088/2041-8205/802/2/L18 |bibcode= 2015ApJ...802L..18L |arxiv= 1503.05554

|s2cid=54179272 |url=http://dro.dur.ac.uk/16298/1/16298.pdf?DDD25+dph1nm+d700tmt}}

Triangulum II is a candidate for detecting WIMPs as a source of dark matter.