|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
Quasar brightness lower bound, real or my error?
For this plot of quasar Mag vs z
https://inspirehep.net/record/120804...dist1_dr10.png There is a lower bound for quasar Mag that looks artificial. At z=0.4 the lower limit is about M = -23. I tried to check if this is due to a lower limit for sdss scope via using CalcTool for apparent to absolute magnitude calculator http://www.calctool.org/CALC/phys/as...star_magnitude apparent Mag limit for sdss is 22 from their site, which yields absolute mag limit at z=0.4 ~4e9 LYr from Ned Wrights calculator. Entering those values, 22 apparent and 4e9 Lyr distance yields a limit of -18.44 Mag. This is 5 Mag brighter than the lower cut off in the plot, Meaning????? Quasars have a sharp lower brightness bound that gets brighter with increasing z???? What am I doing wrong? rt [[Mod. note -- Could it be that you're seeing Malmquist bias? (https://en.wikipedia.org/wiki/Malmquist_bias) Without doing the numbers I can't see whether this is what you're seeing here, but it would result in just such an observational-selection "sharp lower brightness bound that gets brighter with increasing z". -- jt]] |
#2
|
|||
|
|||
Quasar brightness lower bound, real or my error?
In article ,
writes: For this plot of quasar Mag vs z https://inspirehep.net/record/120804...dist1_dr10.png There is a lower bound for quasar Mag that looks artificial. At z=0.4 the lower limit is about M = -23. Quasars are often DEFINED as AGN brighter than -23. That probably explains your puzzle. |
#3
|
|||
|
|||
Quasar brightness lower bound, real or my error?
On Monday, December 26, 2016 at 12:31:03 PM UTC-5, wrot=
e: For this plot of quasar Mag vs z=20 =20 https://inspirehep.net/record/120804...dist1_dr10.png =20 {snip} What is the source of this figure? My guess would be that the text of the document in which it appears will answer your question; it could be a selection effect, due to the definition of quasar the authors used, or something else (or some combo). I find it's a good idea to read the text of the document in which such figures (plots) appear, and when asking questions, quote the source. |
#4
|
|||
|
|||
Quasar brightness lower bound, real or my error?
Thanks Jonathan,
Yes, it does look like Malmquist bias and has the right sense. But it's off by 5 magnitudes....too dim. ie, the scope should be able to see far dimmer objects. So there shouldn't be a cut off, at least not on that graph at that brightness value....based on my calculations Sooooo, I'm guessing my calculations are wrong but can't see why. rt [[Mod. note -- Could it be that you're seeing Malmquist bias? (https://en.wikipedia.org/wiki/Malmquist_bias) Without doing the numbers I can't see whether this is what you're seeing here, but it would result in just such an observational-selection "sharp lower brightness bound that gets brighter with increasing z". -- jt]] |
#5
|
|||
|
|||
Quasar brightness lower bound, real or my error?
In article ,
writes: On Monday, December 26, 2016 at 12:31:03 PM UTC-5, wrot= e: For this plot of quasar Mag vs z=20 =20 https://inspirehep.net/record/120804...dist1_dr10.png =20 {snip} What is the source of this figure? My guess would be that the text of the document in which it appears will answer your question; it could be a selection effect, due to the definition of quasar the authors used, or something else (or some combo). I find it's a good idea to read the text of the document in which such figures (plots) appear, and when asking questions, quote the source. From the paper: "this quasar sample is flux limited to i = 19.1". |
#6
|
|||
|
|||
Quasar brightness lower bound, real or my error?
On Wednesday, December 28, 2016 at 10:37:20 AM UTC-5, Phillip Helbig
(undress to reply) wrote: {snip} From the paper: "this quasar sample is flux limited to i = 19.1". Thanks PH. I found a copy of the paper, Shen+ (2013), as an arXiv preprint: https://arxiv.org/abs/1212.4526 rt: Does knowing that the sample is flux limited ("to i = 19.1") answer the question you asked? |
#7
|
|||
|
|||
Quasar brightness lower bound, real or my error?
On Monday, January 2, 2017 at 10:04:26 PM UTC-8, wrote:
On Wednesday, December 28, 2016 at 10:37:20 AM UTC-5, Phillip Helbig (undress to reply) wrote: {snip} From the paper: "this quasar sample is flux limited to i = 19.1". Thanks PH. I found a copy of the paper, Shen+ (2013), as an arXiv preprint: https://arxiv.org/abs/1212.4526 rt: Does knowing that the sample is flux limited ("to i = 19.1") answer the question you asked? Yes, I think that is what I was missing from the start. Makes perfect sense now, thanks. rt |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Mars Bound Spacecraft Example | [email protected] | Policy | 37 | March 4th 16 09:55 AM |
#32 Luminet team made an error just as Johns Hopkins made an error on | [email protected] | Astronomy Misc | 2 | May 16th 08 06:43 AM |
Bound water on Mars. | Robert Clark | Astronomy Misc | 0 | June 19th 07 05:22 PM |
The Real Bible Code - Decoding in Real Time | [email protected] | Astronomy Misc | 0 | April 28th 06 03:40 PM |
Sorry guys there's bound to be cloud .......... | Alan | UK Astronomy | 5 | January 20th 04 07:03 PM |