Un quasar derrière NGC 2650 ?

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JP Nougayrede
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Joined: Tue Oct 20, 2015 8:33 pm

Un quasar derrière NGC 2650 ?

Post by JP Nougayrede »

Bonsoir,

Pour jouer avec le spectro Alpy sur le ciel profond, j'ai visé ce quasar catalogué comme vu à travers la galaxie NGC 2650.
C'est une cible sympa en guise d'exercice de style pour dépoussiérer le matériel, un entrainement aussi pour une supernova.
Mais le résultat me surprend un peu !?

La cible :
Carto.jpg
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D'après le catalogue Milliquas (The Million Quasars (Milliquas) catalogue, version 7.2 (Flesch, 2021)
http://vizier.cds.unistra.fr/viz-bin/Vi ... cno=520494
Rmag = 11.00 mag / ? Red optical magnitude (4)
Bmag = 17.00 mag / ? Blue optical magnitude (4)
z = 1.900 / ? Redshift from the literature or esti...

La position de la fente
Guide_31x5sec_level.jpg
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Le spectre, avec un C11@f7, Alpy 600, caméra CCD414, 6x600 sec, calibration sur lampe alpy et étoile HD 70313
QJ08500701.png
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Le spectre ne ressemble pas à celui d'un quasar, plutôt à une étoile + la galaxie ? On peut jouer avec les z du quasar et de la galaxie pour identifier des raies, mais ça me semble curieux quand même pour un objet à Rmag 11. Qu'en pensez vous ?

Jean-Philippe
etienne bertrand
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Joined: Mon Aug 31, 2015 11:26 am

Re: Un quasar derrière NGC 2650 ?

Post by etienne bertrand »

Salut JP,
A priori d'accord avec toi c'est un spectre stellaire avec les raies du MgI et NaI visibles. Sur l'image on a l'impression aussi que ça ressemble fortement à une étoile.
Tu peux écrire un mail à la base de données SIMBAD tu auras une réponse même si parfois ça me du temps.
Bon travail en tout cas !
Robin Leadbeater
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Re: Un quasar derrière NGC 2650 ?

Post by Robin Leadbeater »

Interesting ! The reference for the redshift comes from this paper on X ray sources
https://ui.adsabs.harvard.edu/abs/2008A ... K/abstract
where it calls it “QSO east of NGC 2650”

They say in the paper

“The X-ray quasar 1RXS J085001.4 + 701804 is an interesting object. This quasar shines through the outer disk of the spiral galaxy NGC 2650. We see absorption lines from the foreground galaxy in the quasar spectrum as a result of this projected superposition.”

There is also an optical spectrum there in fig 11 where it calls it a star and a spectrum of NGC2650.

Perhaps there is also an X ray source at the same position which is the QSO ?
ngc2650_quasar.png
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ngc2650.png
ngc2650.png (55.99 KiB) Viewed 6360 times
Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
JP Nougayrede
Posts: 152
Joined: Tue Oct 20, 2015 8:33 pm

Re: Un quasar derrière NGC 2650 ?

Post by JP Nougayrede »

Thanks Robin.

In this paper, the spectrum "NGC 2650 (star)" would be that of the quasar ? If so, my spectrum does not match, as I do not see the emission lines around 4500 and 6000. Looking at their spectrum, it is not clear to me how could they deduce a z=1.9 in table 3. Edit : two broad emission lines at ~8100 and ~4500 could be that of Mg II and CIV at z 1.9
Capture d’écran 2022-05-11 155328.jpg
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Active galactic nuclei can emit X rays. Reading the paper, the Rosat X ray source is "interesting" : it is very, very, bright at 10E46 erg/s (by far the brighest of that in the list shown in the table, by at least two logs). The calculated absolute magnitude is close to -29; again that's very bright, even for a quasar.

Active galactic nuclei can also be bright in the infrared. In the NED database, the X source is quasi coincident with Wise source WISEA J085010.58+701758.1
https://ned.ipac.caltech.edu/conesearch ... h%20center

Ok it is an interesting object but still a bit mysterious for me !
etienne bertrand
Posts: 1040
Joined: Mon Aug 31, 2015 11:26 am

Re: Un quasar derrière NGC 2650 ?

Post by etienne bertrand »

for me too !
Robin Leadbeater
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Re: Un quasar derrière NGC 2650 ?

Post by Robin Leadbeater »

No the spectrum of the object labelled "star" is just a foreground star. The paper is confusing but I think the resolution of ROSAT was not good enough to say exactly where the X-Ray source was so they measured the spectrum of all visible objects in the region. (the galaxy and the foreground star) Clearly neither are the quasar. The coordinates and the redshift in the catalogue are the coordinates of the foreground star, incorrectly taken from the paper assuming it related to the quasar but I have not been able to find any earlier references to the z=1.9 quasar with absorption from ngc2650 mentioned in the paper

Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Robin Leadbeater
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Re: Un quasar derrière NGC 2650 ?

Post by Robin Leadbeater »

ngc2650 is also an AGN so perhaps that is an X-Ray source ?
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
JP Nougayrede
Posts: 152
Joined: Tue Oct 20, 2015 8:33 pm

Re: Un quasar derrière NGC 2650 ?

Post by JP Nougayrede »

Thanks again for your insight Robin. I think you're right, the paper is rather imprecise on the observation and exact localisation of the quasar. The reviewers missed that before publication ;)
I should have taken a spectrum of the galaxy core, and the other stars in the vicinity. The galaxy is hiding behind some trees for me, so maybe next year.
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