M–sigma relation

<h2 id="origin">Origin</h2>
The tightness of the M–σ relation suggests that some kind of feedback acts to maintain the connection between black hole mass and stellar velocity dispersion, in spite of processes like <a href="/facts/Galaxy_merger/WRKsV7t2">galaxy mergers</a> and <a href="/facts/Accretion_(astronomy)/atcWRsDP">gas accretion</a> that might be expected to increase the scatter over time.
One such mechanism was suggested by <a href="/facts/Joseph_Silk/yNDIJ0dT">Joseph Silk</a> and <a href="/facts/Martin_Rees/aaIpNneA">Martin Rees</a> in 1998.<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a> These authors proposed a model in which supermassive black holes first form via collapse of giant 
gas clouds before most of the bulge mass has turned into stars. The black holes created in this way would then accrete and radiate, driving a wind which acts back on the accretion flow.
The flow would stall if the rate of deposition of mechanical energy into the infalling gas was large enough to unbind the protogalaxy in one crossing time. The Silk and Rees model predicts 
a slope for the M–σ relation of α = 5, which is approximately correct. However, the predicted normalization of the relation is too small by about a factor of one thousand. The reason is that there is far more energy released in the formation of a supermassive black hole than is needed to completely unbind the stellar bulge.
A more successful feedback model was first presented by <a href="/facts/Andrew_King_(astronomer)/l9L1k9Uc">Andrew King</a> at the <a href="/facts/University_of_Leicester/Q0vDtHV7">University of Leicester</a> in 2003.<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a> In King's model, feedback occurs through momentum transfer, rather than energy transfer as in the case of Silk & Rees's model. A "momentum-driven flow" is one in which the gas cooling time is so short that essentially all the energy in the flow is in the form of bulk motion. In such a flow, most of the energy released by the black hole is lost to radiation, and only a few percent is left to affect the gas mechanically. King's model predicts a slope of α = 4 for the M–σ relation, and the normalization is exactly correct; it is roughly a factor c/σ ≈ 103 times larger than in Silk & Rees's relation.

<h2 id="importance">Importance</h2>
Before the M–σ relation was discovered in 2000, a large discrepancy existed between black hole masses derived using three techniques.<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a>
Direct, or dynamical, measurements based on the motion of stars or gas near the black hole seemed to give masses that averaged ≈1% of the bulge mass (the "Magorrian relation"). Two other techniques—<a href="/facts/Reverberation_mapping/B5tEoost">reverberation mapping</a> in <a href="/facts/Active_galactic_nuclei/qT1owvXz">active galactic nuclei</a>, and the <a href="/facts/So%C5%82tan_argument/Ixrm0Lf0">Sołtan argument</a>, which computes the cosmological density in black holes needed to explain the <a href="/facts/Quasar/HS96328l">quasar</a> light—both gave a mean value of M/Mbulge that was a factor ≈10 smaller than implied by the Magorrian relation. The M–σ relation resolved this discrepancy by showing that most of the direct black hole masses published prior to 2000 were significantly in error, presumably because the data on which they were based were of insufficient quality to resolve the black hole's dynamical <a href="/facts/Sphere_of_influence_(black_hole)/Dzcn0kNy">sphere of influence</a>.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a> The mean ratio of black hole mass to bulge mass in big early-type galaxies is now believed to be approximately 1 : 200, and increasingly smaller as one moves to less massive galaxies.
A common use of the M–σ relation is to estimate black hole masses in distant galaxies using the easily measured quantity σ. Black hole masses in thousands of galaxies have been estimated in this way. The M–σ relation is also used to calibrate so-called secondary and tertiary mass estimators, which relate the black hole mass to the strength of emission lines from hot gas in the nucleus or to the velocity dispersion of gas in the bulge.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a>
The tightness of the M–σ relation has led to suggestions that every bulge must contain a supermassive black hole. However, the number of galaxies in which the effect of the black hole's gravity on the motion of stars or gas is unambiguously seen is still quite small.<a class="footnote-ref" id="fnref:15" href="#fn:15">15</a> It is unclear whether the lack of black hole detections in many galaxies implies that these galaxies do not contain black holes; or that their masses are significantly below the value implied by the M–σ relation; or that the data are simply too poor to reveal the presence of the black hole.<a class="footnote-ref" id="fnref:16" href="#fn:16">16</a>
The smallest supermassive black hole with a well-determined mass has Mbh ≈ 106 M☉.<a class="footnote-ref" id="fnref:17" href="#fn:17">17</a>[needs update] The existence of black holes in the mass range 102–105 M☉ ("<a href="/facts/Intermediate-mass_black_hole/eAm6Hqe0">intermediate-mass black holes</a>") is predicted by the M–σ relation in low-mass galaxies, and the existence of intermediate-mass black holes has been reasonably well established in a number of galaxies that contain <a href="/facts/Active_galactic_nuclei/qT1owvXz">active galactic nuclei</a>, although the values of Mbh in these galaxies are very uncertain.<a class="footnote-ref" id="fnref:18" href="#fn:18">18</a>
No clear evidence has been found for ultra-massive black holes with masses above 1010 M☉, although this may be an expected consequence of the observed upper limit to σ.<a class="footnote-ref" id="fnref:19" href="#fn:19">19</a>

<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Faber%E2%80%93Jackson_relation/DSzRl9np">Faber–Jackson relation</a></li>
<li><a href="/facts/Galaxy_formation_and_evolution/uAPtXxr4">Galaxy formation and evolution</a></li>
<li><a href="/facts/Sigma-D_relation/5RtAueNI">Sigma-D relation</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Merritt, David (1999). "Black holes and galaxy evolution". In Combes, F.; Mamon, G. A.; Charmandaris, V. (eds.). Dynamics of Galaxies: from the Early Universe to the Present. Vol. 197. Astronomical Society of the Pacific. pp. 221–232. arXiv:astro-ph/9910546. Bibcode:2000ASPC..197..221M. ISBN 978-1-58381-024-8. <a href="978-1-58381-024-8" target="_blank">978-1-58381-024-8</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">Ferrarese, F. and Merritt, D. (2000), A Fundamental Relation between Supermassive Black Holes and Their Host Galaxies, The Astrophysical Journal, 539, L9-L12 <a href="/wiki/David_Merritt" target="_blank">/wiki/David_Merritt</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">Gebhardt, K. et al. (2000), A Relationship between Nuclear Black Hole Mass and Galaxy Velocity Dispersion, The Astrophysical Journal, 539, L13–L16 <a href="http://adsabs.harvard.edu/abs/2000ApJ...539L..13G" target="_blank">http://adsabs.harvard.edu/abs/2000ApJ...539L..13G</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">Kormendy, John; Ho, Luis C. (2013) Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies <a href="http://adsabs.harvard.edu/abs/2013ARA%26A..51..511K" target="_blank">http://adsabs.harvard.edu/abs/2013ARA%26A..51..511K</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">Davis, B.L., et al. (2017), Updating the (supermassive black hole mass)-(spiral arm pitch angle) relation: a strong correlation for galaxies with pseudobulges <a href="http://adsabs.harvard.edu/abs/2017MNRAS.471.2187D" target="_blank">http://adsabs.harvard.edu/abs/2017MNRAS.471.2187D</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">McConnell, N. J. et al. (2011), Two ten-billion-solar-mass black holes at the centres of giant elliptical galaxies, Nature, 480, 215–218 <a href="http://adsabs.harvard.edu/abs/2011Natur.480..215M" target="_blank">http://adsabs.harvard.edu/abs/2011Natur.480..215M</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">Magorrian, J.; Tremaine, S.; Richstone, D.; Bender, R.; Bower, G.; Dressler, A.; Faber, S. M.; Gebhardt, K.; Green, R.; Grillmair, C.; Kormendy, J.; Lauer, T. (1998). "The Demography of Massive Dark Objects in Galaxy Centers". The Astronomical Journal. 115 (6): 2285–2305. arXiv:astro-ph/9708072. Bibcode:1998AJ....115.2285M. doi:10.1086/300353. S2CID 17256372. <a href="/wiki/John_Magorrian" target="_blank">/wiki/John_Magorrian</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">Savorgnan, Giulia A. D.; Graham, Alister W. (2015), Overmassive black holes in the MBH-σ diagram do not belong to over (dry) merged galaxies <a href="http://adsabs.harvard.edu/abs/2015MNRAS.446.2330S" target="_blank">http://adsabs.harvard.edu/abs/2015MNRAS.446.2330S</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">Giulia A.D. Savorgnan, et al. (2016), Supermassive Black Holes and Their Host Spheroids. II. The Red and Blue Sequence in the MBH-M*,sph Diagram <a href="http://adsabs.harvard.edu/abs/2016ApJ...817...21S" target="_blank">http://adsabs.harvard.edu/abs/2016ApJ...817...21S</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Silk, J. and Rees, M. (1998), Quasars and galaxy formation, Astronomy and Astrophysics, 331, L1–L4 <a href="http://adsabs.harvard.edu/abs/1998A%26A...331L...1S" target="_blank">http://adsabs.harvard.edu/abs/1998A%26A...331L...1S</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">King, Andrew (2003). "Black Holes, Galaxy Formation, and the MBH-σ Relation". The Astrophysical Journal. 596 (1): L27 – L29. arXiv:astro-ph/0308342. Bibcode:2003ApJ...596L..27K. doi:10.1086/379143. S2CID 9507887. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">Merritt, D. and Ferrarese, L. (2001), Relationship of Black Holes to Bulges [1] <a href="http://nedwww.ipac.caltech.edu/level5/March01/Merritt3/frames.html" target="_blank">http://nedwww.ipac.caltech.edu/level5/March01/Merritt3/frames.html</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">Merritt, David (2013). Dynamics and Evolution of Galactic Nuclei. Princeton, NJ: Princeton University Press. ISBN 9781400846122. <a href="9781400846122" target="_blank">9781400846122</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">Peterson, B. (2008), The central black hole and relationships with the host galaxy, New Astronomy Reviews, 52, 240–252 <a href="http://adsabs.harvard.edu/abs/2008NewAR..52..240P" target="_blank">http://adsabs.harvard.edu/abs/2008NewAR..52..240P</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
<li id="fn:15">Batcheldor, D. (2010), "The M–σ Relation Derived from Sphere of Influence Arguments", The Astrophysical Journal, 711 (2): L108 – L112, arXiv:1002.1705, Bibcode:2010ApJ...711L.108B, doi:10.1088/2041-8205/711/2/L108, S2CID 118559296 <a href="/wiki/Daniel_Batcheldor" target="_blank">/wiki/Daniel_Batcheldor</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></li>
<li id="fn:16">Valluri, M. et al. (2004), Difficulties with Recovering the Masses of Supermassive Black Holes from Stellar Kinematical Data, The Astrophysical Journal, 602, 66–92 <a href="http://adsabs.harvard.edu/abs/2004ApJ...602...66V" target="_blank">http://adsabs.harvard.edu/abs/2004ApJ...602...66V</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></li>
<li id="fn:17">Merritt, David (2013). Dynamics and Evolution of Galactic Nuclei. Princeton, NJ: Princeton University Press. ISBN 9781400846122. <a href="9781400846122" target="_blank">9781400846122</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></li>
<li id="fn:18">Ho, L. (2008), Nuclear activity in nearby galaxies, Annual Review of Astronomy & Astrophysics, 46, 475–539 <a href="http://adsabs.harvard.edu/abs/2008arXiv0803.2268H" target="_blank">http://adsabs.harvard.edu/abs/2008arXiv0803.2268H</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></li>
<li id="fn:19">Batcheldor, D. et al. (2007), How Special Are Brightest Cluster Galaxies?, The Astrophysical Journal, 663, L85–L88 <a href="/wiki/Daniel_Batcheldor" target="_blank">/wiki/Daniel_Batcheldor</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></li>
</ol>

M–sigma relation open-in-new

M–sigma relation