Editing BL Lacertae object (section)

==Host galaxies==

[[Image:ESO Centaurus A LABOCA.jpg|thumb|right|250px|[[Centaurus A]], the closest BL Lac object to the Milky Way.<ref name=Chiaberge>{{cite journal | url=https://ui.adsabs.harvard.edu/abs/2001MNRAS.324L..33C/abstract | bibcode=2001MNRAS.324L..33C | title=The BL Lac heart of Centaurus A | last1=Chiaberge | first1=M. | last2=Capetti | first2=A. | last3=Celotti | first3=A. | journal=Monthly Notices of the Royal Astronomical Society | date=2001 | volume=324 | issue=4 | pages=L33–L37 | doi=10.1046/j.1365-8711.2001.04642.x | doi-access=free | arxiv=astro-ph/0105159 }}</ref>]]

Soon after the discovery of this unusual class of objects it was noted that the sources were surrounded by a faint nebulosity. In the late 1970s the use of modern detectors (such as [[Charge-coupled device|CCD]]) allowed observers to probe with better accuracy the nature of the nebulosity. First images of the BL Lac object PKS 0548-322 by [[Mike Disney|Michael John Disney]] in 1974 in various filters found it to be composed by a giant elliptical galaxy with a bright nucleus.

Extensive surveys taken with the [[Hubble Space Telescope]] of 132 BL Lac objects comprising seven complete radio, X-ray, and optically selected samples in 2000 studied the morphologies of possible BL Lac host galaxies. The data concluded that in two-thirds of the BLL images taken, host galaxies are detected, including in nearly all with [[redshift]] z < 0.5. BL Lac objects are luminous enough that only one quarter (6/22) of the images taken with z > 0.5 were resolved because of relatively short exposure times.<ref name=":1" /> A de Vaucouleurs profile <math>I(R)\propto R^\frac14</math><ref>{{Cite book|title=Galaxies in the Universe: An Introduction|first1=L. S.|last1=Sparke|author1-link=Linda Sparke|first2= J. S. III|last2= Gallagher|publisher=[[Cambridge University Press]]|year=2007|isbn=978-0-521-67186-6|location=Cambridge University|pages=244}}</ref> looks to be a significantly preferred brightness profile for 58 of the 72 resolved host galaxies at over ~99% confidence. The results of this survey conclude that there is an 8% limit to the number of disk systems in BL Lac objects and is therefore consistent with the assumption that all BL Lac host galaxies could be elliptical. These ellipticals are very luminous with a median absolute K-corrected [[Absolute magnitude|magnitude]] of <math>M_R\thicksim-23.7\pm-0.6</math> mag (rms dispersion). This is comparable to the brightest cluster galaxies.<ref name=":1">{{Cite journal|last=Urry|first=Megan|year=2000|title=The Hubble Space Telescope Survey of BL Lacertae Objects|journal=The Astrophysical Journal|volume=523|issue=2|pages=816–829|doi=10.1086/308616|bibcode=2000ApJ...532..816U|arxiv=astro-ph/9911109}}</ref>