Tuesday, December 21, 2010


Saw the total lunar eclipse early Tuesday morning. Sweet.

Then attended Jesse Rogerson's public talk and Master's defense. He passed with specified revisions to the thesis (and numerous compliments on the talk). Discussed turning the thesis into a paper, and next steps for our mutual research.

Monday, December 20, 2010


Friday: Paola Rodriguez-Hidalgo visited my group at York. Much discussion of quasars and Mg II absorbers ensues. Jesse Rogerson gives practice thesis talk.

Monday: met with my grad students, and with Alireza Rafiee to discuss response to referee report on the sub-Eddington boundary. Spent afternoon doing my share of revising the text and sent the resulting draft to Alireza.

Thursday, December 16, 2010


Backed up files to JungleDisk and to a new external HDD. Summarized a few papers on Shareflow, including the key Dexter & Agol paper on quasar accretion disks with inhomogeneous temperature distributions.

Wednesday, December 15, 2010

Back at York

Met with Ali Rafiee and Laura Chajet for brief research (and teaching) discussions; reviewed Jesse Rogerson MSc thesis presentation draft.

Also, just for fun, looked up eight unidentified quasar candidates from the Large Bright Quasar Survey in the SDSS: one spectroscopically confirmed star, three stars confirmed by nonzero proper motions, three BL Lac objects, and one probable transient that is now much fainter than it was when the LBQS candidates were selected.

Tuesday, December 14, 2010

Back in Toronto

Back in Toronto. Have had short discussions with Jesse Rogerson about refining his Mg II equivalent width analysis and about his Master's thesis presentation. Short Skype meeting with Laura Chajet. Commented on newest revisions to draft PHL 1811 analog paper.

Thursday, December 9, 2010


Last day at OSU. Wrote online summaries of some papers, transferred others over from Google Wave.

Wednesday, December 8, 2010

Two days

Tuesday: sort papers & write notes on some. Chat w/Brad Peterson. Spectral measurements on new HET spectra for PHL 1811 analog paper.

Wednesday: sort papers & write notes on some. Final revised FBQS J1408+3054 paper off to MNRAS and arXiv. Skype w/Laura - turns out the erroneous analytic solution for inhomogeneous covering hasn't affected any published results, as the integral in question has been evaluated numerically. Skype w/Jesse - turns out the problem of accounting for EW measurement upper limits and uncertainties is "ridiculously simple, like most riddles when you see the answer", to quote Gandalf.

Monday, December 6, 2010


Today and parts of Saturday and Sunday were spent sorting research papers in my office, skimming/reading some of them, and writing online summaries of some. Quite a few could be recycled after writing summaries (and some before).

Friday, December 3, 2010

Catch-up post

Wednesday: final comments on Jesse Rogerson Master's thesis before distribution to committee; email to Gordon Richards and Nic Kruczek re: their paper draft; comments on Ali Rafiee research statement.

Thursday and Friday: PHL 1811 analog draft commenting and thinking. Office sorting. Laura Chajet Skype meeting.

Wednesday, December 1, 2010

Sub-Eddington Boundary 1

Here are my thoughts on arXiv:1011.6381 'Comment on "Biases in the Quasar Mass-Luminosity Plane' by Steinhardt & Elvis, which is a response to Rafiee & Hall arXiv:1011.1268. The original sub-Eddington boundary (SEB) paper is Steinhardt & Elvis 2010a.

These are my thoughts, not those of Alireza Rafiee (first author on our paper, who recently completed his PhD with me). I am posting them publicly as a personal experiment in 'open science'; feel free to send the URLs of this or any subsequent post around to all and sundry. Comments may be posted publicly or sent to me and Ali privately.

SUMMARY: Steinhardt & Elvis make some good points about where we could be clearer, but also make two mistakes (in section 1 and section 2). However, they do raise a valid issue regarding the definition of the SEB: I was thinking of the SEB as having a slope different from unity, but they have a valid point that a SEB with a slope of unity is still a SEB. By that definition, we do find a SEB at low redshifts, but nowhere does the slope appear significantly different from unity (see section 3 discussion below).

Going through the posting by S&E:

Section 1. "Statistical Significance:"

S&E say "The claim that the SEB disappears at z ∼ 2 rests entirely upon this small value of gamma." That is incorrect. In section 2 of our paper, specifically Figure 3, we show that the Rafiee & Hall (ApJS, submitted) BH masses measured using the line dispersion of MgII do not show a SEB with slope different from unity (see further discussion in Section 3 below). That result does not depend on gamma being less than 2; in fact, gamma = 2 for Fig. 3. Where gamma comes in is in section 4 & Figure 7, where we show that recalibration of the Shen et al. mass scale can eliminate the SEB.

S&E are quite correct that there is a large dispersion in gamma from different fitting techniques, but MLINMIX_ERR is the only method which considers intrinsic scatter and errors on both parameters, making it the optimal method and the one on which we base our conclusions. (e.g., we could have included least-squares fitting ignoring individual error bars in Table 2, but its inclusion wouldn't make its results worthy of consideration.)

That said, S&E are also correct that the MLINMIX_ERR gamma=1.27+-0.40 is not different from the canonical gamma=2 at a statistically significant level. We say this right before section 4.1, and our conclusions stand. (Though I would consider changing the statement in the conclusion that the SEB "is likely not a real boundary" to "is quite possibly not a real boundary". The point being that until we can constrain gamma much more tightly, we won't know for sure.)

Section 2. "Non-Virial Motions:"

S&E say that we "do not assume that motions in the quasar broad-line region are predominantly virial (i.e. M_BH \propto (v_virial)^2 \propto FWHM^2)". That's a misinterpretation of Wang et al. 2009, whose analysis we follow. Basically, Wang et al. point out that if Hbeta and MgII don't come from the same part of the BLR, then you can have M_BH(RM) \propto (sigma_Hbeta,rms)^2 \propto (FWHM_MgII)^gamma, where gamma != 2 (and where "RM" stands for reverberation mapping); see our Eqs. 1 and 2. It's true that if there are nonvirial motions, then allowing gamma != 2 helps account for them, but they don't need to exist for gamma != 2 to be correct. Note that Wang et al. find gamma=1.70+-0.42 whereas we find gamma=1.27+-0.40. Luis Ho (personal communication) has found that the SEB slope is not significantly different from unity using the Wang et al. mass calibration.

Section 3

S&E raise a valid issue regarding the definition of the SEB: I was thinking of the SEB as a boundary below Eddington _with slope different from unity_, but they have a point that a SEB with a slope of unity is still a SEB. We will need to rephrase our paper to be in line with this proper definition of a SEB.

By this definition, we do find a SEB at low redshifts, but nowhere does the slope appear significantly different from unity. That is, we find that the 95th percentile value of the Eddington ratio appears to be a function of redshift but independent of mass. (I'm saying "appears" until we measure the 95% values and compute the slopes.)

S&E consider this result by itself to be a puzzling limit on quasar accretion, and they could well be right. My gut reaction is that a mass dependence is more puzzling than a redshift dependence, but my gut could well be wrong. One natural idea is that a redshift dependence could be a result of downsizing, with BHs in general being fueled less at lower redshift. But while it's conceptually easy to understand the Eddington limit boundary (quasar luminosity saturates above a M_BH-dependent mass accretion rate) and a SEB with slope zero (maximum mass accretion rate independent of M_BH leads to maximum luminosity), other boundaries are harder to understand. A M_BH-independent 95th percentile Eddington ratio away from the Eddington limit corresponds to different physical mass accretion rates, so what prevents accretion above that rate for a given BH from occurring? The same goes for a SEB with nonunity slope.

On another note, near the end of the section S&E say "In SE10 we showed the entire redshift range (z = 0.2 to 4.1) allowed by our sample and techniques. RH10 should do the same." In fact we do; our use of only MgII-based masses and our fitting requirement of modeling the FeII emission from 2200-3000 Ang means that we cover a more limited redshift range than SE10.

Section 4

* Our Fig. 1 was intended to serve only as an introduction to the SEB, like Fig. 3 of SE10, not to illustrate the full redshift-dependent extent of the SEB (for which we use Figs 2, 3 and 7). To clarify this, we need to either edit the caption or change the figure to show only quasars in one redshift bin.

* The captions to our Figs 3 and 7 mention that the differences in the M-L plane are particularly noticeable at high redshift. We should rewrite these captions accounting for the discussion of the SEB definition in the Section 3 comments above.

* S&E are quite correct here; they do indeed discuss the possibility of a mass-dependent BH mass correction in their section 4.5.2, and we will need to rewrite our discussion accordingly.

Section 5

I agree that "it is important to continue to improve our understanding of virial mass estimation" and that "Rafiee & Hall do not claim statistically significant deviations from virial masses". However, our new calibrations do show a SEB slope which is consistent with unity, unlike what was found by SE10.

What Next?

I'm making my grad student Jesse Rogerson think about next steps following from his Master's Thesis, so I feel obligated to do the same. What do we need to make progress on these issues? Roughly in order of perceived usefulness:

* Reverberation mapping in MgII and Hbeta simultaneously, to put MgII masses on a more empirical footing and to better constrain gamma (targets need to be at redshift high enough that MgII is visible from ground)
* Next best way to constrain gamma would be simultaneous snapshot spectra of MgII and Hbeta in previously reverberation-mapped AGN (e.g. with STIS and COS in next HST cycle?), to compare single-epoch sigma_MgII and single-epoch sigma_Hbeta; the scatter between single-epoch sigma_Hbeta and sigma_Hbeta,rms has been characterized (Denney et al. 2009)
* Apply R&H10 PCA-reconstruction MgII BH mass technique to full DR7 (about to start)
* extend R&H10 PCA-reconstruction BH mass technique to Hbeta and CIV, intercalibrating masses where Hbeta+MgII or MgII+CIV are both available

Tuesday, November 30, 2010

Catch-up post

Thanksgiving holiday: email exchange with Laura Chajet about modeling inhomogeneous absorption; she has found an error in the original formulation of these models which may require redoing quite a bit of published work. Also ported a lot of Google Wave reviews of published astro papers to Zenbe Shareflow.

Monday: read revised bits of Jesse Rogerson's Master's thesis. Read 1st draft of a followup C IV / X-ray paper by Gordon Richards' student Nic Kruczek, and drafted email to them. Read Steinhardt & Elvis' comment on the paper Alireza Rafiee & I put on astro-ph earlier this month. They have some good suggestions for clarification, some mistakes, and one good point for us to consider.

Tuesday: sent a few more comments to Jesse. Spent lots of time fixing proofs for MNRAS paper on FBQS J1408+3054. I'm paying the price for being lazy and not using natbib. But I've now figured out how to use natbib for MNRAS (basically, use mn.bst and not mn2e.bst).

Tuesday, November 23, 2010

Daily Update; BAL EW vs. time for transverse motion

Finished & sent note to Fred Hamann about arXiv:1008.3728. Finished one last task for grant report.

An idea inspired by Guido Risaliti's recent OSU colloquium: if you have BAL region "clouds" which are rotating in the same sense as the accretion disk, and if the accretion disk follows the Hubeny et al. models where the rotationally approaching half of the disk is brighter than the receding half, you might be able to verify those models by looking at BAL EWs vs. time. (Assuming also that the transverse motion of the BAL is dominated by rotation.) As a BAL cloud first moves in front of the disk, the absorption EW should increase rapidly, as the part of the disk being covered is the bright, approaching half. In other words, for an absorber gradually covering the whole continuum source, a depth halfway to maximum absorption should be reached in less than half the time to maximum absorption (equivalently, at half the time to maximum absorption, the depth will be more than halfway to maximum). For a BAL cloud moving out of our LOS to the continuum source, from complete covering to zero covering, the recovery to continuum will happen faster in the 1st half of the uncovering timescale than in the 2nd half.

Monday, November 22, 2010

Daily Update

As alluded to in the previous post, today I read Morabito et al. 1011.4327 and sent a quick note to the authors. Also I read Hamann et al. 1008.3728 (variability in a high-velocity quasar NAL system) and started writing a quick note to Fred. Also followed up on an email to Hans-Walter Rix about quasar variability. Also got email from Chris Churchill with MgII EW numbers for a lensed quasar for Jesse; still waiting for similar numbers on another system from George Djorgovski. Also filled in a progress report (including some budgeting) for my Ontario Early Researcher Award.

Average density in BAL X-ray absorbers

Astronomy over the weekend included fixing a factor of 2 numerical error in my most recent paper (which fortunately hasn't gone to press yet). A question from Joe Shields led me to think about density and column density limits in the outflow in FBQS J1408+3054. By crude analogy to a similar FeLoBAL with published high-resolution spectra and X-ray data (J0300+0048), the Fe II column density lower limit is uninteresting. But if the total column density in this object is Compton thick with N_H >= (10^24 cm^-2)/Z where Z is the metallicity relative to solar, then the average density of the X-ray absorber must be >~(10^4 cm^-3)/fZ where f is its filling factor along the line of sight. For example, if the X-ray absorber (which is likely not identical to the UV absorber) extends from the BH out to 1/10th the distance of the UV BAL gas, then its density has to be >~(10^5 cm^-3)/Z. If the X-ray absorber extends farther from the BH than the UV absorber, then f>1 in the above and the density can be lower. But too much of the X-ray absorber exterior to the UV absorber will cause Compton scattering of the quasar's UV continuum and remove it from sight.

Update: Morabito et al. 1011.4327 today reinforce the above by pointing out that in FeLoBALs studied to date, f<<1 because the X-ray absorber must be interior to the UV continuum emitting region or else it would Thomson scatter the UV continuum out of our line of sight. For the 1.4E8 Msun BHs in that paper, R_Sch = 4E13 cm and 20R_Sch=8E14 cm. For a column N_H=(1E25 cm^-2)/Z located interior to that radius, the average density is 1E25/8E14 = (1.25 x 10^10 cm^-3)/Z.

Friday, November 19, 2010

Gamma-ray NLS1s, BAL spectra

A check of the HST archive reveals that none of the five narrow-line Seyfert 1 galaxies (NLS1s) detected to date in gamma-rays (all at redshifts < 1) have HST spectra. These AGN are very likely to be within a few degrees of face-on to their accretion disks, and we can see broad emission lines from them, so we have a rare opportunity to study broad line profiles at a known inclination angle. Sounds like an HST proposal to me.

Other recent activities have included:
a Skype conversation with my student Laura Chajet;
simple reductions of MDM spectroscopy of a variable BAL quasar to see if it its variability is ongoing (it's not, unfortunately);
a bit of digging around in papers on Hanny's Voorwerp or related subjects;
and realizing there's a factor of two error in my latest first-author paper (d'oh!) ...fortunately, once the error is corrected the result is more interesting rather than less, and the paper's still at the proofs stage and so the error can be corrected before it is printed. That won't endear me to the MNRAS staff, but I think I'll request to be sent a paper to referee as a way of making amends.

Wednesday, November 17, 2010

PHL 1811 analogs, Thesis, Postdoc

For the PHL 1811 analog paper: replaced a file; analyzed an HST spectrum; reconsidered a redshift; added a sentence on testing a speculative explanation.

Read and commented on Jiang & Goodman's arXiv:1011.3541 paper on star formation in quasar accretion disks (well written, but a modest step forward, not a great leap).

Rogerson Master's Thesis delivered to supervising committee; Skype conversation with Jesse mapping out refinements to the analysis to tackle next.

Budgeted for postdoc and other research expenses over the next few years, and wrote email answering queries about my offer to my first-choice postdoc applicant.

Quasars: Some Answers, More Questions

Here is a PDF version of the talk I gave yesterday at Ohio University. If you want to see the simulation by Kurosawa & Proga in action, click on the density (zoom) movie here. If you want to see the animation of the disappearing FeLoBAL trough, click here.

Monday, November 15, 2010

Weekend: PHL 1811 analogs, Mg II absorption

Dug up some old information on PHL 1811 analogs for the forthcoming paper, and wrote a few more sentences about them. Also continued to review drafts of Jesse Rogerson's Master's Thesis, plus did some investigation of MgII data in other quasar asterisms. Began adopting old colloquium into new version for talk at Ohio University tomorrow.

Friday, November 12, 2010

Cross-matched SDSS quasar catalogs

I've been toiling off and on for a few days on cross-matching various SDSS quasar catalogs. Thought I had it all sewn up Tuesday night, but realized Wednesday morning that I'd been using the UNIX 'uniq' command incorrectly. After fixing that I thought I was finished Thursday morning; then I remembered I wanted to cross-match another catalog, and in so doing I identified some discrepancies it took me the rest of the day to track down and fix.

But today the cross-matched catalogs are available online for anyone to use. I only ask that you read the Readme file! More catalogs will probably be cross-matched in the future.

Other activities:
* have been making comments on drafts of Jesse Rogerson's Master's Thesis
* Guido Risaliti visited this week so I attended the colloquium he gave, had dinner with him and Brad Peterson, and chatted with him a bit about AGN science
* usual daily Astro Coffee and Friday Journal Club meetings
* also read "Carrots and Sticks: Unlock the Power of Incentives to Get Things Done" by Ian Ayres, which isn't astronomy but which I plan to apply to astronomy (among other things) as soon as I digest it a bit further

Monday, November 8, 2010

Weekend Update (PHL 1811 Analogs, sub-Eddington Boundary)

Science over the weekend and through today so far has focused on thinking some more about PHL 1811 analogs (intrinsically X-ray weak quasars), about which Niel Brandt, his grad student Jianfeng Wu and I (and collaborators) are preparing a paper.

I also prepared some materials in support of a colleague's NSF proposal.

Lastly, my former grad student Ali Rafiee had a paper on astro-ph (it's still astro-ph to me, not arXiv) today showing that the reported sub-Eddington boundary is not seen in our analysis of quasar black hole masses vs. luminosities. Reaction here at Ohio State (and by email from another member of the community) has been positive; Occam's Razor is on our side!

Friday, November 5, 2010

Week On, Week Off

I was on vacation from last Thursday afternoon through Tuesday afternoon; only work-related item done was to send off a reference letter for my former grad student Ali Rafiee. Wednesday through Friday of this week was spent catching up on email, advising my student Jesse Rogerson on his Master's thesis, and reading through the job applications and reference letters for the postdoctoral fellowship I've advertised to work with me at York starting next year. I narrowed it down to a shortlist of six people, including my first choice and the runner-up, and made an offer to my first choice today. It's likely the decision won't be finalized until early next year, after the results of prestigious fellowship competitions are announced, but I'm pleased with the shortlisted applicants.

Wednesday, October 27, 2010

Cometary BAL Clouds?

If BAL clouds have optically thick cores surrounded by lower column density envelopes, then the envelopes will be more affected by radiation pressure than the cores and will be accelerated outwards from the quasar more than the core of the cloud will. This might form a tail analogous to a comet's dust tail, trailing the cloud opposite to its direction of motion. Such an effect might be detectable by looking to see if variable BAL troughs get stronger more quickly than they get weaker. That is, as a cometary BAL cloud moves across our line of sight, it should first produce a sharp jump in absorption from the core, followed by a slower decline from the larger envelope. That kind of variability was seen in X-rays by Maiolino et al. [that's where I got the idea] and in the UV at one point in FBQS 1408+3054 (see the 3rd-5th data points in Figure 3 of my paper); the SDSS DR5 and DR6 BAL catalogs should have many more examples to use to look for this effect (should also check the Gibson et al. 2008 and 2010 papers to see if they've already looked for this in their datasets).

Crap, is it Wednesday Already?

Recent activities include:

* conference call with Niel Brandt and his grad student Nur Filiz Ak about targeted BAL variability studies in SDSS-III
* useful exercise of writing a units conversion program (e.g., how many grams/second is a mass loss rate of 1 solar mass/year?)
* writing a macro version of my SM code for generating animated gif movies of BAL variability (now including the uncertainties in interpolated spectra, calculated using the observed sqrt[1-exp(-t/tau)] increase to a maximum sigma of 0.23 magnitudes over a timescale tau of 101 rest-frame days)
* experimenting with the Shareflow website as a Google Wave replacement for collaborative commenting on astronomy papers

Right now I am reading & commenting a draft of my grad student Jesse Rogerson's Master's Thesis. (Finished that; had a Skype meeting w/Jesse about it, and a Skype meeting w/my other grad student Laura; read & commented on a draft paper from my former grad student Alireza.)

Monday, October 25, 2010

Working for the Weekend

Friday's work included the previous blog post and, after
an epic battle with SM, the creation of a generic macro for plotting a
quasar spectrum with logarithmic wavelength axes in both quasar and rest frames.

Sunday included tinkering with with an MDM telescope proposal,
and getting lots of minor items crossed off my to-do list. Good times.

Friday, October 22, 2010

Color (or Colour) Variability of BAL Quasars

Here's a summary of ideas for studying BAL quasar variability.

Most BAL trough variability comes from transverse motion of absorbing clouds. The timescale of variation constrains the clouds' transverse velocity. That provides a constraint on the cloud's distance from the black hole (via angular momentum conservation plus the fact that a disk wind's terminal velocity is a few times the circular velocity at its launch radius). Uncertainties on the transverse velocity translate directly to uncertainties on the distance; thus, we want to accurately measure transverse velocities of BAL clouds, which requires spectroscopy during a trough variability event.

It is fairly common to see that BAL troughs _have_ varied, but much less common to see them actually vary. That is, either trough changes are very quick so that we almost never see them happening or they are very gradual so that we only notice them after sufficient time has passed. The two possibilities can be discriminated using time series photometry of BAL and non-BAL quasars (e.g., SDSS Stripe 82).

First, a prediction: trough variability will cause BAL quasars to show more color variability than non-BAL quasars, as measured by some variant of the structure function S: if you have N individual measurements i of an object's color c, then S = [\sum_i \sqrt{c_i^2 - sig_i^2}]/N, where sig is the uncertainty on the color.
Problem: colors aren't like magnitudes; a zero or negative color is perfectly reasonable.  What needs to be measured is whether or not the distribution of color measurements differs from that expected from random variations due to noise.  So probably best to just use reduced chi^2:
\chi_\nu^2=[\sum_i (c_i-c_0)^2 / sig_i^2]/(N-1), where c_0 is the mean color of the object.  Now if the c_i values are drawn from Gaussian distributions with variance sig_i^2, then on avg. \chi_\nu^2 = 1, and if there is colour variability, it will be larger.  But what matters is the distribution of \chi_\nu^2 for BALs and nonBALs - we expect the distributions to be different.  However, a complication is that the \chi_\nu^2 distribution changes as N increases, so you can't intercompare \chi_\nu^2 values from objects with different N.  So I'm thinking we should just use the distribution of individual \chi_i^2 = (c_i-c_0)^2/sig_i^2.  By plotting the distribution of all those individual values for nonBAL quasars (each with a different c_0 of course), and then the equivalent distribution for BAL quasars, we should see a difference.
[In fact, may want to just plot distribution of \chi=(c_i-c_0)/sig_i, to retain maximum information.  An object with a few outlying large negative \chi values may not be the same as an object with a few outlying large positive \chi values, but could have an indistinguishable \chi^2 distribution.  So that's a reason for using just \chi.]
(Note that a quick look at the Stripe 82 dataset shows that some method for excluding outliers (X sigma from the median color for each quasar?) needs to be implemented before calculating \chi_i^2.)

A refined prediction is that some subset of BAL quasars will show more color variability than non-BALs; any BALs which only show absorption from distant (kpc-scale) gas will show variability consistent with non-BALs, but BALs with pc-scale gas will show more color variability. (One would also have to keep an eye out for objects which were non-BALs during a past spectroscopic epoch but which later developed a BAL trough.)

The \chi or \chi_i^2 distribution won't answer the question of BAL trough variability timescales; to do so, I think you need to look at the distribution of the rate of colour changes r_ij=(c_j-c_i)/(t_j-t_i) where the t values are the rest-frame times of observation. If trough variations are slow, you'll have lots of small values of r_ij. If trough variations are fast, you'll have lots of even smaller values of r_ij, plus a few large values. (One complication is that the uncertainty on r_jk will be correlated with that on both r_ij and r_kl. A crude workaround is to separate each quasar into two datasets: ij in 1, jk in 2, kl in 1, lm in 2, etc., so errors are uncorrelated within each dataset.) One would have to compare the BAL colour change rate distribution to that of non-BALs, as colour changes caused by trough variability will be in addition to any intrinsic colour variability (e.g., quasars usually get slightly bluer when they get brighter). And comparisons should be done in bins of similar rest-frame wavelength [<- most important], luminosity and black hole mass, [and BAL subtype (Hi/Lo/FeLo) and maybe Eddington ratio] to remove any effects of those parameters on intrinsic variability and to search for any dependency of trough variability on those parameters.

A plot of c_j-c_i vs. t_j-t_i for all i,j pairs would also be useful to see just how fast color changes of a given magnitude can happen.

If that timescale is not too short, then it might be worth monitoring BAL quasars photometrically to catch new cases of trough variability as they start to happen and then trigger spectroscopic followup. It might be possible to demonstrate the feasibility of such an approach using SDSS: establish a threshold of |delta_c/sig_c| > 3 (say), look for quasars whose delta_c/sig_c exceeds that threshold _after_ a spectroscopic epoch in which the quasar appears as a non-BAL, and then look for the subset of objects with a 2nd epoch spectrum after that color change. The 2nd epoch spectrum should show a new BAL, or other unusual effect like a transient increase in reddening or strong emission line variation.

I'll link back to this post y/o post a comment if/when I pick up this idea again. It's worth doing, but I need to finish other projects first.

Thursday, October 21, 2010

BAL quasars

Bit more research chatting with OSU grad students.

Skype conversation with my grad student Laura Chajet, about fitting absorption troughs.

Worked on two new cases of BAL variability from SDSS-III, including adapting existing software to more easily deal with SDSS-III spectra. Time spent writing code now will pay off in not having to repeat the same processing steps in the future (obvious, yes; but when I'm teaching I find I opt for the what's-quickest-now approach instead of what's-best-in-the-long-run).

Investigated whether a list of BALs bright enough for MDM spectroscopy have pre-existing X-ray observations. Some do, making them good targets for spectroscopic monitoring (and a 2nd epoch of X-ray data if their troughs are seen to vary).

Wednesday, October 20, 2010

Tue-Wed Oct 19-20

Met with Matthias Dietrich & Smita Mathur about observing proposal to monitor bright BAL quasars.

Discussed paper on variable BAL quasar at Astro Coffee; general interest among AGN folk in the paper and in searching for similar objects in light-curve datasets.

Skype meeting with my grad student Jesse Rogerson.

Isolated, downloaded and examined 135 SDSS-III repeat spectra of BAL quasars. Found one new case of dramatic variability!

Monday, October 18, 2010

Monday Oct. 18th

Read the latest draft of a paper on PHL 1811 analogs (intrinsically X-ray-weak quasars), and did some measurements on the spectra of possibly similar moderately X-ray-weak quasars, which turn out to appear intermediate in other properties as well.

Posted the recently accepted paper on arXiv.org; it should appear in Tuesday evening's mailing.

Switched desks in my office at Ohio State.

Friday, October 15, 2010

Historical Photometry of BAL quasars

The paper on dramatic variability in a BAL quasar that I submitted last week to MNRAS (see Wed. Oct. 6 post) is now accepted; look for it on arXiv next week.

York undergrad Ted Rudyk visited Wednesday and Thursday. We were investigating whether old photographic magnitudes could be used to look for other cases of 'overlapping trough' BAL quasars transitioning between heavily absorbed (red) and unabsorbed (blue) states. We found a few cases of potential long-term variations in BAL trough strength as traced by g-r color (see graph for SDSS J090212.4+592415 above), but we're limited by the photometric accuracy of the old POSS-I and DPOSS magnitudes. My colleague Zeljko Ivezic and his former grad student Branimir Sesar have produced recalibrated photographic magnitudes for quasars from SDSS DR2, but there are no plans to extend the recalibration to DR7 quasars. If such a recalibration did get done, we could look at long-term quasar color variability in BAL vs. non-BAL quasars, including searching for quasars which aren't BALs now but were in the past. Could also take a stab at this using SDSS Stripe 82 data from Zeljko's current grad student Chelsea MacLeod.

Ted and I talked to Smita Mathur and Matthias Dietrich about possible BAL variability projects with the MDM 2.4-meter telescope to which OSU has access. Biweekly to monthly monitoring of quasars with high-velocity outflows and known X-ray properties seems to be the best bet.

Talked to Phil Hopkins about searching for radial inflow (with ALMA and in quasar spectra) as a signature of the single-armed spiral waves that feed AGNs in his simulations.

On Friday gave this journal club on distance measurements to BAL outflows.

Tuesday, October 12, 2010

Monday & Tuesday

Played around with SDSS-III spectra to familiarize myself with data access. Already have one cool result I can't post because the data isn't public yet.

Wrote referee reports for two Gemini proposals.

Spent a bit of time thinking about PHL 1811 analogues.

Spent time discussing research with grad students and visiting postdoc Phil Hopkins.

Friday, October 8, 2010

Rest of Friday

Refereed a Canada-France-Hawaii Telescope proposal.

Discussed some plots over at my grad student Jesse Rogerson's research blog.

Looked at some talks from this summer's Accretion Processes in X-Rays Workshop.

Retrieved SDSS magnitudes & epochs of overlapping trough BALs for Ted Rudyk.

Past 48 hours

Not quite yet in the habit of daily posts.

Spent part of Wed. evening conferring with York undergrad Ted Rudyk about a nascent project to look for historical variability of "overlapping-trough" FeLoBALs like FBQS J1408+3054 seen in the previous post's animated gifs.

Thursday and Friday up till now spent in extremely productive conversations with colloquium visitor Daniel Proga (UNLV), who does numerical simulations of disk winds. Started my review of the literature on disk winds and quasars in general with his papers. The goal is to refresh my picture of how quasars work; to aid in this I am investigating the Papers software as well as other ways of disseminating research thoughts (like this blog).

Wednesday, October 6, 2010

Revised FBQS 1408 paper submitted

Today I submitted this revised paper to MNRAS. The gist of the paper is shown in the animated gif below. The animation shows the spectrum of the BAL quasar FBQS 1408+3054 from 1995 to 2009 (black curves are data, grey curves are interpolations). Note that starting sometime after 2000, the Fe II absorption starts to go away. (more below animation)

The disappearing Fe II absorber is even more remarkable when historical photographic-plate photometry is taken into account. That photometry shows that this quasar is consistent with having been an FeLoBAL quasar for 50 years before its Fe II absorber vanished over a period of 5 years. That history is shown schematically in the animated gif below (which takes a while to run).

(Other activities today so far included submission of merit exercise paperwork to York and going around and introducing myself to some of the grad students and postdocs here at OSU and asking about their research.)

Tuesday, October 5, 2010


This blog is intended to keep my students, collaborators and other interested parties up to date with my astronomy research activities.

For example, today I put the finishing touches on a paper for MNRAS (Monthly Notices of the Royal Astronomical Society) about a broad absorption line (BAL) quasar whose singly-ionized Fe II absorption region disappeared. This is the first time an FeLoBAL (Iron Low-Ionization BAL) quasar has been seen to change into a LoBAL.

You can read quick summaries of most of my recent research interests