Author Topic: Presenting - the People's Choice spectra!  (Read 7073 times)

NGC3314

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Re: Presenting - the People's Choice spectra!
« Reply #15 on: July 21, 2010, 08:35:06 pm »
The immediate sign of rotation in the wisp galaxy is the "tilt" of the H-beta emission line, a systematic change in its observed wavelength (and thus redshift, Doppler included) from one side to the other. Here are a couple of closeups, both grayscale and contour; I smoothed it by a 1.5-pixel (sigma) Gaussian to make it clearer for a noisy spectrum. In each case, wavelength increases to the right, and location along the slit goes up-down. Looking at the mean wavelength of emission from the line in 3-pixel (about 2-arcsecond) segments, we see this:

Pixels    Wavelength Doppler offset (km/s)
192-194  4968.95  -59
195-197 4969.37  -33
198-200 4970.43   +31
201-203 4973.10   +192
204-206 4973.10   +192

The Doppler offset is relative to the location of peak emission in the spectrum (which is not necessarily the galaxy nucleus), with the mean redshift taken out, and represents the component of mean orbital motion in the disk along our line of sight at that position. The total velocity range is typical for galaxies of modest luminosity; the Milky Way would show about +/- 250 km/s if we viewed it edge-on. The more face-on we see a galaxy, the smaller the line-of-sight component becomes.

EigenState

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Re: Presenting - the People's Choice spectra!
« Reply #16 on: July 21, 2010, 10:54:01 pm »
The immediate sign of rotation in the wisp galaxy is the "tilt" of the H-beta emission line, a systematic change in its observed wavelength (and thus redshift, Doppler included) from one side to the other.
Thank you!  If my interpretation of the "tilt"is correct, that would correspond to an asymmetric line profile if presented as line intensity as a function of wavelength as per our conventional SDSS spectral plots.

Best regards,
ES

NGC3314

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Re: Presenting - the People's Choice spectra!
« Reply #17 on: July 22, 2010, 03:40:57 am »
The immediate sign of rotation in the wisp galaxy is the "tilt" of the H-beta emission line, a systematic change in its observed wavelength (and thus redshift, Doppler included) from one side to the other.
Thank you!  If my interpretation of the "tilt"is correct, that would correspond to an asymmetric line profile if presented as line intensity as a function of wavelength as per our conventional SDSS spectral plots.

It can, but need not. The SDSS spectra integrate over an optical fiber which spans 3 arcseconds of sky, and all information on spatial structure in, for example, line wavelengths, is lost. If you look at a symmetric galaxy with a disk tilted to our line of sight, the integrated line profile will be symmetric (ignoring for the moment such complications as dust) but placing a slit across the appropriate direction will show a relation between position and Doppler shift. How that translates to the line profile in a more realistic case depends on the total intensity of the line at each wavelength within the field of the fiber.

Radio astronomers have dealt with this for decades in measuring H I emission from spiral galaxies, many of which are smaller than the beam size of a single-dish antenna. They often see a characteristic "double-horn" profile, as material over large regions on either "end" of the tilted disk projects to similar velocities and piles up in the line profile. One could see this effect optically for, say, H-beta when observing galaxies so distant as to be unresolved by a spectrograph (it shows up when synthetically replicating such a spatially-integrated profile from slit spectra).

Rick Nowell

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Re: People's Choice spectra - a Markarian and its sidekick
« Reply #18 on: July 27, 2010, 11:21:14 am »
This is a blazingly bright one - Rick Nowell suggested this blob (SDSS 587733608012316682 ) just to the north of the starburst galaxy Markarian 490.

Is this another blob galaxy next to MRK 0193?
http://cas.sdss.org/dr6/en/tools/explore/obj.asp?id=587731891114803230


SIMBAD gives both a very similar redshift, but labels it as an HII object. NED lists it as a galaxy. It is mentioned in one
paper (http://iopscience.iop.org/0004-637X/662/1/15/pdf/0004-637X_662_1_15.pdf), but I have not yet located its spectra.

Its Markarian big brother has been posted on the forum several times in Markarian galaxies, the most weird OIII objects
and Wolf-rayet galaxies.
http://cas.sdss.org/dr6/en/tools/explore/obj.asp?id=587731891114803229

zutopian

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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).

Warning: this topic has not been posted in for at least 120 days.:
The above post is from July 2010, but there are papers, which were submitted later (but there are also papers submitted before), about that QSO.:

I mention just the following two papers, but there are more after July 2010.:

HS 1700+6416: the first high redshift non lensed NAL-QSO showing variable high velocity outflows
Quote
We present a detailed analysis of the X-ray emission of HS 1700+6416, a high redshift (z=2.7348), luminous quasar, classified as a Narrow Absorption Line (NAL) quasar on the basis of its SDSS spectrum. The source has been observed 9 times by Chandra and once by XMM from 2000 to 2007.
Authors: G. Lanzuisi, M. Giustini, M. Cappi, M. Dadina, G. Malaguti, C. Vignali, G. Chartas
(Submitted on 30 May 2012)
http://arxiv.org/abs/1205.6587

‘Sideline quasars’ helped to stifle early galaxy formation, says CU study:
http://www.colorado.edu/news/releases/2013/03/21/%E2%80%98sideline-quasars%E2%80%99-helped-stifle-early-galaxy-formation-says-cu-study
The above article is about following paper.:
The He II Post-Reionization Epoch: HST/COS Observations of the Quasar HS 1700+6416
Authors: David Syphers, J. Michael Shull
(Submitted on 6 Dec 2012)
http://arxiv.org/abs/1212.1502


PS: Attachments of the GZ spectra can be find in the original post.
« Last Edit: April 30, 2013, 08:14:56 am by zutopian »