REVIEW
Local Ultraluminous Infrared Galaxies and Quasars
Astrophysics · Submitted 1 Mar 2006 · 46 references
Pith's verdict: A careful, transparent review that consolidates the case for ULIRGs as forming ellipticals, but whose key numbers live in in-press companion papers.
T0 · AI review
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Referee report
The paper
The paper claims
The most luminous local galaxy mergers are intermediate-mass ellipticals in formation that are becoming moderate-luminosity optical quasars.
The reading
What carries the argument
The load-bearing diagnostic is the comparison of ULIRG hosts with quasar hosts and inactive spheroids using the photometric fundamental plane of elliptical galaxies — the correlation between surface brightness, half-light radius, and (implicitly) velocity dispersion. ULIRG and PG quasar hosts land on the locus of intermediate-size ($\sim 1$–$2\,L_*$) spheroids, while the hosts of more luminous quasars are systematically larger; this match is what turns the scatter of individual morphological classifications into an evolutionary claim. The second piece of machinery is the merger-driven evolutionary sequence from cool ULIRGs to warm ULIRGs to quasars, where infrared color ($f_{25}/f_{60}$) and AGN signatures track the stage of the merger; galactic winds provide the mechanism that removes the remaining gas at the end of the sequence.
Extended reading notes
Core claim
The central claim is a merger-driven evolutionary sequence: gas-rich disk galaxies merge, pass through an ultraluminous infrared starburst phase, then a dust-enshrouded AGN phase, and finally emerge as optically bright, 'naked' quasars once the gas and dust are consumed or blown away. The evidence assembled here is that AGN activity appears in a substantial fraction of ULIRGs (often dominant in more than 30% of the whole class and more than 50% of those with $\log (L_{\rm IR}/L_\odot) \gtrsim 12.3$); that warm, AGN-like ULIRGs are advanced single-nucleus mergers with prominent spheroids and weak tidal features; that the hosts of ULIRGs and moderate-luminosity PG quasars are statistically indistinguishable in luminosity, size, and surface brightness, both falling near the photometric fundamental plane of intermediate-mass ($\sim 1$–$2\,L_*$) ellipticals; and that coalesced ULIRGs match intermediate-mass ellipticals in stellar velocity dispersion and rotation-to-dispersion ratio, implying black hole masses of order $10^7$–$10^8\,M_\odot$. Galactic winds, detected in virtually all ULIRGs, with outflow velocities of a few hundred km s$^{-1}$ and energetics up to $10^{59}$ erg, provide a plausible feedback mechanism for shedding the excess gas that would otherwise leave the system looking like a circum-nuclear starburst rather than a naked quasar.
Load-bearing premise
The argument assumes that the resemblance between ULIRG hosts and quasar hosts is a time-ordered, evolutionary connection rather than a coincidence between two unrelated populations, and that these hosts are dynamically relaxed enough that single-component light-profile fits and measured velocity dispersions describe the stellar spheroid rather than a young, unrelaxed merger remnant.
Editorial extensions
If this is right
- Most local ULIRGs are local analogs of the high-redshift mergers that build intermediate-mass spheroids and feed their black holes, so their detailed study is a direct probe of spheroid and black-hole growth.
- Coalesced ULIRGs should leave behind intermediate-mass black holes of order $10^7$–$10^8\,M_\odot$ in spheroids of roughly $10^{11}\,M_\odot$, a specific prediction for the local remnant population.
- The winds detected in virtually all ULIRGs are energetic enough to remove the remaining gas, making feedback from starbursts and AGN observationally testable in real systems rather than only in simulations.
- Because some late-merger ULIRGs show no quasar activity and some low-luminosity quasars contain disks, the merger-to-quasar route is efficient only above a luminosity threshold; below it, other fueling mechanisms must operate.
Reading between the lines
- A testable extension: if the sequence is real, the descendants of local ULIRGs should be quiescent intermediate-mass ellipticals with weak tidal features and slightly young or blue central stellar populations; a targeted search for such remnants could confirm the genealogy.
- The luminosity threshold implied by the disk-bearing low-luminosity PG quasars predicts that the merger route dominates only above roughly $10^{12}\,L_\odot$; below that, disk instabilities or minor mergers may be the main triggers, a prediction that can be checked by comparing host morphologies across luminosity.
- If winds clear the gas in essentially every ULIRG, the post-coalescence drop in star formation rate should be visible in spatially resolved stellar populations of nearby remnants, offering an independent test of the feedback picture.
Original abstract
This paper reviews the recent results from a comprehensive investigation of the most luminous mergers in the local universe, the ultraluminous infrared galaxies (ULIRGs) and the quasars. First, the frequency of occurrence and importance of black hole driven nuclear activity in ULIRGs are discussed using the latest sets of optical, near-infrared, mid-infrared, and X-ray spectra on these objects. Obvious trends with luminosity, infrared color, and morphology are pointed out. Next, the host galaxy properties of ULIRGs are described in detail and then compared with local quasar hosts and inactive spheroids. By and large, these data are consistent with the scenario where ULIRGs are intermediate-mass elliptical galaxies in formation and in the process of becoming moderate-luminosity optical quasars. The powerful galactic winds detected in many ULIRGs may help shed any excess gas during this transformation. However, this evolutionary scenario does not seem to apply to all ULIRGs and quasars: Ultraluminous infrared mergers do not always result in a quasar, and low-luminosity quasars near the boundary with Seyferts do not all show signs of a recent major merger.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
This paper reviews the recent results from a comprehensive investigation of the most luminous mergers in the local universe, the ultraluminous infrared galaxies (ULIRGs) and the quasars. First, the frequency of occurrence and importance of black hole driven nuclear activity in ULIRGs are discussed using the latest sets of optical, near-infrared, mid-infrared, and X-ray spectra on these objects. Obvious trends with luminosity, infrared color, and morphology are pointed out. Next, the host galaxy properties of ULIRGs are described in detail and then compared with local quasar hosts and inactive spheroids. By and large, these data are consistent with the scenario where ULIRGs are intermediate-mass elliptical galaxies in formation and in the process of becoming moderate-luminosity optical quasars. The powerful galactic winds detected in many ULIRGs may help shed any excess gas during this transformation. However, this evolutionary scenario does not seem to apply to all ULIRGs and quasars: Ultraluminous infrared mergers do not always result in a quasar, and low-luminosity quasars near the boundary with Seyferts do not all show signs of a recent major merger.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | This paper reviews the recent results from a comprehensive investigation of the most luminous mergers in the local universe, the ultraluminous infrared galaxies (ULIRGs) and the quasars. | contribution 0.92 | 0.35 | 0.05 | asserted 0.79 |
| s1 | First, the frequency of occurrence and importance of black hole driven nuclear activity in ULIRGs are discussed using the latest sets of optical, near-infrared, mid-infrared, and X-ray spectra on these objects. | contribution 0.70 | 0.33 | 0.03 | asserted 0.65 |
| s2 | Obvious trends with luminosity, infrared color, and morphology are pointed out. | result 0.99 | 0.69 | 0.03 | asserted 0.99 |
| s3 | Next, the host galaxy properties of ULIRGs are described in detail and then compared with local quasar hosts and inactive spheroids. | contribution 0.91 | 0.58 | 0.04 | asserted 0.81 |
| s4 | By and large, these data are consistent with the scenario where ULIRGs are intermediate-mass elliptical galaxies in formation and in the process of becoming moderate-luminosity optical quasars. | interpretation 0.99 | 0.38 | 0.76 | hedged possibility 0.99 |
| s5 | The powerful galactic winds detected in many ULIRGs may help shed any excess gas during this transformation. | interpretation 0.98 | 0.26 | 0.05 | hedged possibility 1.00 |
| s6 | However, this evolutionary scenario does not seem to apply to all ULIRGs and quasars: Ultraluminous infrared mergers do not always result in a quasar, and low-luminosity quasars near the boundary with Seyferts do not all show signs of a recent major merger. | limitation 0.60 | 0.47 | 0.17 | hedged possibility 0.57 |
What was examined, and what was not
- arXiv listing abstract v1
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- references and citing sentences
- relations to other papers
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References
Discussion
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