HST images of quasars


The Host Galaxies of Three Radio-Loud Quasars: 3C 48, 3C 345, and B2 1425+267
Author(s):Sofia Kirhakos, John N. Bahcall, Donald P. Schneider, and Jerome Kristian
Journal: ApJ, 520, 67-77 (July 20, 1999); astro-ph/9902175

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Abstract: Observations with the Wide-Field/Planetary Camera-2 of the Hubble Space Telescope (HST) are presented for three radio-loud quasars: 3C 48 (z = 0.367), B2 1425+267 (z = 0.366), and 3C 345 (z= 0.594). All three quasars have luminous (~4 × L*) galaxies as hosts, which are either elliptical (B2 1425+267 and 3C 345) or interacting (3C 48), and all hosts are 0.5 - 1.0 mag bluer in (V-I) than other galaxies with the same overall morphology at similar redshifts to the quasars. The host of
3C 48 has many H II regions and a very extended tidal tail. All nine of the radio-loud quasars studied here and in Bahcall et al. (1997) either have bright elliptical hosts or occur in interacting systems. There is a robust correlation between the radio emission of the quasar and the luminosity of host galaxy; the radio-loud quasars reside in galaxies that are on average ~1 mag brighter than hosts of the radio-quiet quasars.

Hubble Space Telescope (HST) images of twenty nearby luminous quasars
Author(s): John N. Bahcall, Sofia Kirhakos, David H. Saxe, and Donald P. Schneider
Journal:The Astrophysical Journal, 479, 642-658 (April 20, 1997); astro-ph/9611163

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Abstract: Observations with the Wide-Field Camera of the Hubble Space Telescope (HST) are presented for a representative sample of 20 intrinsically luminous quasars with redshifts smaller than 0.30. These observations show that luminous quasars occur in diverse environments that include ellipticals as bright as the brightest cluster galaxies (2), apparently normal ellipticals (10), apparently normal spirals with H~II regions (3), complex systems of gravitationally interacting components (3), and faint surrounding nebulosity (2).

The quasar host galaxies are centered on the quasar to the accuracy of our measurements, 400 pc. Some of the host galaxies show no evidence of merging or strong gravitational interactions. There are more radio quiet quasars in galaxies that appear to be ellipticals (7) than in spiral hosts (3), contrary to expectations. However, three, and possibly five, of the six radio loud quasars have detectable elliptical hosts, in agreement with expectations. Strong upper limits are placed on the possible existence of optical jets. The luminous quasars studied in this paper occur preferentially in luminous galaxies. The average absolute magnitude of the hosts is 2.2 magnitudes brighter than expected for a field galaxy luminosity function.

The superb optical characteristics of the repaired HST make possible the detection of close galactic companions; we detect eight companion galaxies within projected distances of 10~kpc from the quasars. The presence of very close companions, the images of current gravitational interactions, and the higher density of galaxies around the quasars suggest that gravitational interactions play an important role in triggering the quasar phenomenon.

HST images of twenty nearby luminous quasars
Author(s): John N. Bahcall, Sofia Kirhakos, and Donald P. Schneider
Journal: in Quasar Hosts, proceedings of the ESO-IAC Conference, Tenerife, 24--27 September 1996 (Springer Verlag: Heidelberg), pp. 37--44.

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Abstract: We present observations with the Hubble Space Telescope for a representative sample of 20 intrinsically luminous quasars with redshifts smaller than 0.30. These observations show that luminous quasars occur in diverse environments, including ultra-luminous ellipticals, normal ellipticals, spirals with H II regions, complex systems of gravitationally interacting components, and faint nebulosity. The quasar host galaxies are centered on the quasar to the accuracy of our measurements, 400 pc. Contrary to expectations, there are more radio quiet quasars in ellipticals than in spirals. Most of the radio loud quasars are, as expected, in ellipticals. These 20 luminous quasars occur preferentially in galaxies that are more luminous than the typical field galaxies. Eight companion galaxies lie within projected distances of 10 kpc from the quasar nuclei.

Galaxy clustering around nearby luminous quasars
Author(s): Karl B. Fisher, John N. Bahcall, Sofia Kirhakos, and Donald P. Schneider
Journal: The Astrophysical Journal, 468, 469-474 (September 10, 1996); astro-ph/9602078

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Abstract:We examine the clustering of galaxies around a sample of 20 luminous low redshift (z( 0.30) quasars observed with the Wide Field Camera-2 on the Hubble Space Telescope. The HST resolution makes possible galaxy identification brighter than V = 24.5 and as close as 1'' or 2'' to the quasar. We find a significant enhancement of galaxies within a projected separation of ( 100 h-1 kpc of the quasars. If we model the qso/galaxy correlation function as a power law with a slope given by the galaxy/galaxy correlation function, we find that the ratio of the qso/galaxy to galaxy/galaxy correlation functions is 3.8 ± 0.8. The galaxy counts within r < 15 kpc of the quasars are too high for the density profile to have an appreciable core radius ( 100 h-1 kpc). Our results reinforce the idea that low redshift quasars are located preferentially in groups of 10-20 galaxies rather than in rich clusters. We see no significant difference in the clustering amplitudes derived from radio-loud and radio-quiet subsamples.

The apparently normal galaxy hosts for two luminous quasars
Author(s): John N. Bahcall, Sofia Kirhakos, Donald P. Schneider
Journal: The Astrophysical Journal, 457, 557-564 (February 1, 1996); astro-ph/9509031.

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Abstract: Hubble Space Telescope images of PHL 909 (z = 0.171) and PG 0052+251 (z = 0.155) show that these luminous radio-quiet quasars each occur in an apparently normal galaxy. The host galaxy of PHL 909 is an E4 elliptical, which contradicts the common view that radio quiet quasars occur in spiral galaxies. The host of PG 0052+251 is an Sb spiral. Both host galaxies are several tenths of a magnitude brighter than the characteristic Schechter magnitude for field galaxies. The bright HII regions of the host galaxy of PG 0052+251 provide an opportunity to measure directly the metallicty of the host of a luminous galaxy, to set a direct upper limit to the mass of the AGN, and to test stringently the comosological hypothesis that the galaxy and the quasar are both at the cosmological distance indicated by the emission line redshift of the quasar.

When the images of PHL 909 and PG 0052+251 are compared to the HST images of other objects in our sample of 20 luminous quasars (z <= 0.30), it is clear that the local environments of quasars range over a variety of possibilities including luminous ellipticals, normal ellipticals and spirals, complex interacting systems, and faint hosts.

Hubble Space Telescope and MERLIN observations of the jet in 3C 273
Author(s): J. N. Bahcall, S. Kirhakos, D. P. Schneider, R. J. Davis, T. W. B. Muxlow, S. T. Garrington, R. G. Conway, and S. C. Unwin
Journal: The Astrophysical Journal, 452, L91-L93 (October 20, 1995); astro-ph/9509028.

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Abstract:We present red and blue images of the jet of the quasar 3C273 obtained with the WFPC2 on the Hubble Space Telescope as well as a new radio map made with the MERLIN array. The images are of significantly better quality than that of previous data. The two maps are aligned to an accuracy of 0.020''; this accuracy is achieved because both the quasar and the jet are contained in both the radio and optical images. The start of the optical jet is marked by an elongated knot which appears identical at radio and optical wavelengths. Other knots in the optical jet correspond to narrow oblique features within the radio outline. The total width of the smooth emission in the optical jet is 0.7''; the FWHM of the optical knots is 0.3''. The knots may trace the current location of a narrow, perhaps helical jet lying within the outlines of the older radio cocoon.

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