Author Topic: Presenting - the People's Choice spectra!  (Read 6775 times)

NGC3314

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Presenting - the People's Choice spectra!
« on: July 14, 2010, 02:15:40 am »
And here are the data - the "Peoples Choice" spectra from Kitt Peak. To recap, we had some time at the end of several nights when all our SDSS targets were too low (or set) in the west, so we asked Zooites for suggestions for interesting and instructive things to observe. They are now reduced and calibrated, so we'll post the results object by object in this thread.

We used the GoldCam spectrograph on the Kitt Peak 2.1m telescope (so named since that's its color). It has a slit 5 arcminutes long, which we set to a width of 2 arcseconds. Its orientation on the sky is described by the position angle (PA), which defines the angle north through east that it makes in celestial coordinates. PA=0 is north-south, PA-90 is east/west, and so on. A rotation by 180 degrees has the same effect as flipping the spectrum on the axis along the slit. To set the position angle, we physically rotated the spectrograph using a hand crank attached to a precision readout, unclamping and clamping three locks to make sure it didn't move afterward. For balance reasons, this could be done only while pointing to the zenith, so we didn't do it when we didn't need to set a specific angle for a certain target. As a result, for some of these we kept the orientation of the previous target if it made reasonable sense for the new one. The wavelength resolution (full width at half maximum, FWHM) of these spectra is typically about 3.0 pixels or 3.7 Angstroms, and the useful data cover from 3272 to 5709 Angstroms.

As shown here in the image displays, the lower end of the spectrum is the end to the east, even if only slightly (PA is restricted for this device to the range 0-180 degrees). These have been calibrated using standard stars to give nominally flux per unit wavelength (in popular but distinctly non-SI units - ergs per square centimeter per second per Angstrom). For unresolved objects (stars and quasars) we extract the spectra and present a plot, one-dimensional FITS file, and 2-column text table of wavelength and flux ready to put into a spreadsheet. For galaxies, we show the spectrum, give a 2-dimensional FITS file, and give measured redshifts and line identifications.

It's possible that additional people will come along and make use of these data, which is one reason for giving the detailed information above. If so, an appropriate reference might be Keel/Chojnowski/Lynn observing at NOAO for Galaxy Zoo.

EigenState

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Re: Presenting - the People's Choice spectra!
« Reply #1 on: July 14, 2010, 02:31:00 am »
...The wavelength resolution (full width at half maximum, FWHM) of these spectra is typically about 3.0 pixels or 3.7 Angstroms...
::)

Good to see some data!

Best regards,
ES

NGC3314

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People's Choice spectra - QSO 1700+4616 at z=2.7
« Reply #2 on: July 14, 2010, 02:38:28 am »
QSO H1700+6416 (SDSS 587725492133560346

This is a particularly bright quasar at substantial redshift, z=2.7, suggested by c_cld. It shows the Lyman alpha forest to advantage. The strong emission peak is Lyman alpha, the strongest emission line of hydrogen, whose native habitat is the deep ultraviolet, at 1215.67 Angstroms. Only at these redshifts can we see it through our atmosphere. The quasar spectrum to its blue is chopped up by myriads of narrow, weak absorption lines, eventually identified with Lyman alpha from less-ionized regions of the hot intergalactic gas. These are between us and the quasar, to absorb its light, so each one is at a smaller redshift and thus appears to the blue side of the quasar emission line. All together, they form the Lyman alpha forest (a bit more explanation may be found here), one of the best ways we have of tracing the large amount of ordinary matter which is spread thinly between the galaxies. A few strong narrow absorption lines show up farther to the red; these are so-called metal-line systems arising mostly in gas associated with galaxies (which has been enriched in such absorbing elements as carbon, aluminum, magnesium). The Kitt Peak 2.1m telescope played a key role in the 1960s (back when it was called the 84-inch telescope), in the hands of Roger Lynds and Alan Stockton, in working out the nature of the Lyman alpha forest as we first saw quasars at redshifts high enough to reveal the phenomenon.

This hour-long spectroscopic exposure was obtained at a position angle of 70 degrees. We're attaching a plot, 2 column txt file of wavelength and intensity, and a FITS file of the extracted spectrum. (Note - the forum software doesn't like attached FITS files. I've tried renaming it *fits.txt, and will see whether downloading and renaming that will preserve the binary parts of the file).


NGC3314

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This is a galaxy we've taken to calling the Bowtie starburst (SDSS 587740714036560047. This was suggested by c_cld. The SDSS image is here:

Our slit was along position angle 150, roughly along the long axis of the central part of this very disturbed system. It's definitely a starburst, with strong, narrow emission lines and the hydrogen absorption lines underlying some of them which are both signs of young stars. Many of the higher-order hydrogen emission lines lie in broader absorption from the stars themselves. It has redshift z=0.01270 (standard deviation of emission-line measures is 0.00013).
   
This sort of "bowtie" structure appears in numerical models of galaxies which have seen a strong and rapid gravitational disturbance (even elliptical galaxies fall for it). This one is rotating; the spectrum shows that the northern side is approaching us relative to the south. There is dust structure splitting the spectrum, becoming more prominent toward the blue as its absorption strengthens.

We're attaching a plot, an image display of the spectrum, and a 2D FITS file of the area around the galaxy. Once again, we work around the forum software by calling the FITS file .txt; at least on a Mac, it can be downloaded and renamed back to .fits and all the values are preserved.

NGC3314

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People's Choice spectra - a Markarian and its sidekick
« Reply #4 on: July 14, 2010, 03:57:22 am »
This is a blazingly bright one - Rick Nowell suggested this blob (SDSS 587733608012316682 ) just to the north of the starburst galaxy Markarian 490.


Our slit was along position angle 150 degrees, just getting the eastern edge of the Markarian galaxy. As its color would suggest, this galaxy is dramatically lit up with star formation. It also looks associated with the Markarian galaxy - their redshifts match closely. The northern companion has z=0.00874 with error 0.00013, while the SDSS spectra for two pieces of Markarian 490 have z=0.0089 and 0.0090, so the relative velocities along our line of sight are 60 km/s on average.

NGC3314

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People's Choice spectra - a mysterious wisp
« Reply #5 on: July 14, 2010, 04:34:37 am »
This mystery object is a green wisp on the edge of an anonymous galaxy, found by Lovethetropics and Tsering (back here).

Probably because of interference from the very bright star to the southeast, the galaxy is not an SDSS object. You can see it on the Explorer tool near this star, which we used to align the slit on position angle 119 degrees. This turned out to be a good plan - the galaxy is pretty faint and we could get it in June only by chasing into twilight soon after sunset, so we never did see it on the TV screen. This spectrum is not one of my best in data quality, but we see H-beta (we know it's not [O III] because it's too far to the blue to for that at any redshift), giving us a redshift z=0.0219. The spectrum rises into the blue, which along with the strength of H-beta tells us this galaxy is forming stars briskly. At that redshift it's not all that big - the part that shows up in the SDSS images is something like 6 kiloparsecs across, less than halfway to the center of the Milky Way from here.

In the spectrum display, it shows up below the spectrum of the bright star - the H-beta emission is the only obvious feature. It has velocity structure - you can see that the part of the galaxy projected toward the star is the side receding from us.

Rick Nowell

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Re: People's Choice spectra - a Markarian and its sidekick
« Reply #6 on: July 14, 2010, 09:22:01 am »
I'm confused! The spectrum attached is the one for MRK490, or for its blazingly-blue companion? The spectrum is named
'MRK490 1200'. If it is a spectrum for 'Rick's Blob', then what I presume to be the OIII line is off the graph! If they are neighbours,
then is the blob interacting with MRK490? It doesn't look like a merger though. Redshift conversion gives a distance of approximately 119, 500, 000 light years, which is 'near'.

Thanks to Prof. Keel for his work. Does anything else happen now?

NGC3314

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Re: Presenting - the People's Choice spectra!
« Reply #7 on: July 14, 2010, 09:31:36 am »
That spectrum is of the object to the N of Mkn 490 (we only caught the very edge of Mkn 490 itself). It does have  really strong emission lines (including [O III]). The similar redshifts show that they could be interacting, and it is common for interactions to be associated with such strongly star-forming galaxies (even in cases which are not merging as we see them).

Rick Nowell

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Re: Presenting - the People's Choice spectra!
« Reply #8 on: July 14, 2010, 11:30:27 am »
Thanks for the explanation. I figure the object is referred to as MRK490 'C' in this comprehensive 1986 paper, which also has spectra:
http://adsabs.harvard.edu/full/1986PASP...98..629D   Perhaps I should have searched for this earlier.

 It confirms though that this is a small galaxy nearby that may well have very high rates of star formation, perhaps as a result of an earlier interaction.
To quote: "The 3 sources [MRK490 'A', 'B' and 'C'] vary widely in excitation with 'C' being of exceptionally high excitation."

EigenState

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Greetings,

Regarding the Bowtie starburst (SDSS 587740714036560047):

...This one is rotating; the spectrum shows that the northern side is approaching us relative to the south. There is dust structure splitting the spectrum, becoming more prominent toward the blue as its absorption strengthens.
I assume this conclusion was drawn predicated upon a qualitative analysis of the lineshapes.

Could you please elaborate on that, and if possible include an expanded plot of a relevant spectral feature that illustrates the salient points?

Best regards,
ES

Lovethetropics

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Re: Presenting - the People's Choice spectra!
« Reply #10 on: July 15, 2010, 01:23:01 am »
Thank you so much Bill and Rick and EigenState.  Well the "mystery green blob" is no more.  Now it's a rotating Markarian?  :o ;D ;D

 *and find lots of asteroids  ;D

NGC3314

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People's Choice spectra - the hot and the cool of it
« Reply #11 on: July 16, 2010, 02:58:09 am »
And one more suggested spectrum - a double star (the western one is SDSS 587729231986426149), suggested by Graham D.

The SDSS spectrum probably blends light from both stars, looking sort of like an F-type star. By extracting the spectra from 2" sections along the slit, we have almost completely separated them. They contrast in color and spectra - the eastern one is brighter at short wavelengths, the western one at longer wavelengths. They are roughly spectral types A and G - if they really belong together in a binary, either the A star is a white dwarf (a type DA with hydrogen atmosphere) or the G star is a giant. On the other hand the spectra suggest a pretty large difference in radial velocity for a binary so far apart, so this could be one of the rarer "optical doubles" which are superimposed from our direction but in fact far apart. Our radial-velocity measures will be a bit affected by the slit not being along position angle 90 degrees, not exactly along the two stars' separation, so that the centroid of starlight in the slit will be slightly different. This should be an effect well under 50 km/s in amplitude, but may be present.

The data are together in a text file as (wavelength, hot star flux, cool star flux). The FITS file has the two spectra extracted into separate lines (once again, rename it to FITS after download).

Lightbulb500

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Re: Presenting - the People's Choice spectra!
« Reply #12 on: July 16, 2010, 11:06:52 am »
Thanks for all the information Bill :D
Its all very exciting :)

Tsering

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Re: Presenting - the People's Choice spectra!
« Reply #13 on: July 16, 2010, 05:52:28 pm »
Thank you so much Bill and Rick and EigenState.  Well the "mystery green blob" is no more.  Now it's a rotating Markarian?  :o ;D ;D

Fabulous to have follow up on all these - many thanks to all concerned!  :) 8) :) 8) :)
Om Tare Tuttare Ture Soha

Lovethetropics

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Greetings,

Regarding the Bowtie starburst (SDSS 587740714036560047):

...This one is rotating; the spectrum shows that the northern side is approaching us relative to the south. There is dust structure splitting the spectrum, becoming more prominent toward the blue as its absorption strengthens.
I assume this conclusion was drawn predicated upon a qualitative analysis of the lineshapes.

Could you please elaborate on that, and if possible include an expanded plot of a relevant spectral feature that illustrates the salient points?

Best regards,
ES

Sorry guys, I seem to be more dense than a neutron trinary.  So the green blob has redshift AND blueshift at the same time?  I thought it was a Markarian galaxy, but now it may be a binary?  How many binaries look green and why would they do that? 
« Last Edit: July 18, 2010, 04:25:32 am by Lovethetropics »

 *and find lots of asteroids  ;D