What could galaxies along the line of sight between Earth and distant objects like quasars have anything to do with those objects themselves? Yet in a remarkable finding, the sightlines to quasars seem to be four times less likely to be populated with galaxies than the sightlines to gamma-ray bursts. Odd? Believe it. “The result contradicts our basic concepts of cosmology, and we are struggling to explain it,” said Jason X. Prochaska (UC-Santa Cruz).
The Swift satellite is the vehicle for this work, which used mission data to study the transient yet bright afterglow of long-duration gamma ray bursts (GRBs). Now the paper, by Prochaska and graduate student Gabriel Prochter, is awaiting publication in Astrophysical Journal Letters, but its appearance as a draft on the arXiv site is already spawning new work attempting to answer its questions.
Working with 15 GRBs, the duo found strong absorption signatures indicating the presence of galaxies along 14 of the GRB sightlines. Such signatures occur because some frequencies are absorbed by the gas associated with a galaxy, providing a marker for the galaxy even when there is little visible evidence. But data from the Sloan Digital Sky Survey showing the incidence of galaxies along the sightlines to quasars had the team expecting fewer than four galaxies.
What causes the higher number relating to GRBs? One possibility among three discussed here may be in the way the intervening galaxy acts as a gravitational lens, enhancing the brightness of the background object. If that lensing produces different effects for quasars than GRBs, this could provide an answer, but Prochaska says gravitational lensing experts tell him such a variation is unlikely to hold up, nor do two other explanations involving galactic dust or dust associated with the GRBs themselves. What’s needed to move on to a more convincing explanation is to extend the GRB sample significantly, using data from the extended Swift mission.
Prochaska would like to quadruple the sample size. A good idea indeed, for as the paper notes: “At present, we have not identiﬁed a satisfactory single explanation for this phenomenon. Our results suggest that at least one of our fundamental assumptions underpinning extragalactic absorption line research is ﬂawed.”
Centauri Dreams note: This is another instance of print publication being significantly anticipated by the online preprint process. As scholarly publishing evolves in digital directions, notice how ideas are refined through online venues from e-mail to mailing list, weblog, authorial archive and pre-print server long before they finally see fixed publication in a journal. The added benefit to preprints is, of course, that the audience of judges for submitted papers is enormously extended, and authors can receive input far more quickly than before.
Comments on this entry are closed.
Wow! This is interesting. But the sample size is extremely small. It could be just a statistical fluctuation. That guy, Prochaska, is right – he should take sample of 100+ objects. And the more the better
Halton Arp must be thrilled. His focus was and is on quasars appearing next to galaxies, but I doubt he’s
complaining too much about GRBs doing similar things.
ship early and ship often. i really appreciate the iterative process that internet connectivity has given to this and other fields of investigation and invention.
Man, this one is bizarre. It might be a fluke, like all the supposed quantised red-shifts Tifft thought he’d found. The quasar alignments or lack thereof seems pretty robust based on a sample of 10,000 or so, but GRBs are hard to catch and observe.
Quasar induced galaxy formation: a new paradigm ?
Authors: D. Elbaz, K. Jahnke, E. Pantin, D. Le Borgne, G. Letawe
(Submitted on 16 Jul 2009)
Abstract: We discuss observational evidence that quasars play a key role in the formation of galaxies starting from the detailed study of the quasar HE0450-2958 and extending the discussion to a series of converging evidence that radio jets may trigger galaxy formation.
The direct detection with VISIR at the ESO-VLT of the 7 kpc distant companion galaxy of HE0450-2958 allows us to spatially separate the sites of quasar and star formation activity in this composite system made of two ultra-luminous infrared galaxies (ULIRGs).
No host galaxy has yet been detected for this quasar, but the companion galaxy stellar mass would bring HE0450-2958 in the local M(BH)-M(stellar bulge) relation if it were to merge with the QSO. This is bound to happen because of their close distance (7 kpc) and small relative velocity (~60-200 km/s).
We conclude that we may be witnessing the building of the M(BH)-M(stellar bulge) relation, or at least of a major event in that process. The star formation rate (~340 Msun/yr), age (~200 Myr) and stellar mass (~7×10^10 Msun) are consistent with jet-induced formation of the companion galaxy.
We suggest that HE0450-2958 may be fueled in fresh material by cold gas accretion from intergalactic filaments. We map the projected galaxy density surrounding the QSO as a potential tracer of intergalactic filaments and discuss a putative detection. Comparison to other systems suggest that inside-out formation of quasar host galaxies and jet-induced galaxy formation may be a common process.
Two tests are proposed for this new paradigm: (1) the detection of offset molecular gas or dust emission with respect to the position of distant QSOs, (2) the delayed formation of host galaxies as a result of QSO activity, hence the two step building of the M(BH)/M(stellar bulge) ratio.
Comments: 15 pages, 8 figures, submitted to Astronomy and Astrophysics
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:0907.2923v1 [astro-ph.CO]
From: David Elbaz [view email]
[v1] Thu, 16 Jul 2009 20:04:06 GMT (430kb)