- Participants: I. Lonoce, Paul Compère, Johannes Löhner-Böttcher, Jihane Moultaka, Matthias Schubert
Description: Starting from a sample of ~1300 galaxies with K<22 selected from the MUSIC-GOODS-South field at 0.7<z<3, the aim of the exercise is to find in the VO-archive optical/near IR spectroscopic data with sufficient high value of the S/N ratio (S/N > 10-15) to perform the measurements of some spectral indices. On the one hand, in order to divide the sample in star-forming and passive galaxies, the measured spectral features will be able to estimate the star formation rate by means of fluxes of some emission lines (such as Balmer lines, in particular Hα) thus completing the information given by the exercise of S. Tamburri based on radio 1.4 GHz flux; on the other hand, for galaxies with detected X-ray emission will be interesting to search for a possible confirmation of the presence of AGN, thanks to typical AGN emission lines (e.g. OIIIλ5007Å, MgIIλ2798Å...) and lines' ratios that can be detected and measured on the spectra. The presence of AGN can in fact contaminate the spectral stellar continuum and absorption lines thus distorting the results of any spectral analysis; in particular, some spectral indices in the region of 4000Å (restframe) can be used to estimate age and metallicity of galactic stellar populations. To be sure that the detected AGN doesn't affect the observed optical/near IR spectra, the exercise will then ask for finding available measures of the the column densities N_H of each sample's galaxy, which can reveal the AGN absorption level (absorbed AGN have N_H ≥ 10²² cm-²).
Steps:
- Opened the original list from Ilaria in TOPCAT
- Created a subset of z<0.15&&z_flag>0. This resulted in 30 sources.
- Took these 30 sources and loaded the list into VOSED to perform a multiple object search against all Spectral services in the VO. We only did this for a small number of objects becaue the search takes some time, to do this for all 1300 objects would take about 12-24 hours - something to try after the workshop!
- VOSED produces tables of results - Data Found and Data not found, plus SEDs for each object.
- The Data Found table was loaded into TOPCAT. This contained columns with Signal to noise information, wavelength resolution information and the spectrum services.
- Noting which spectrum services brought back spectra from the VOSED Data found table, we performed a Multiple SSA search in TOPCAT using the original list of objects (all 1300 sources). Did this against the ESO Spectrum service, and some Hubble Space telescope services.
- The ESO Spectrum service brought back many results from the the ESO GOODs VIMOS and FORS2 campaigns.
- The resulting table of spectra were sent to VOSpec, and we started to analyse which spectra contained the Halpha emission line (depends on the redshift of the galaxy, if H alpha falls within the spectrum wavelength ranges).
- Thanks to VOspec tools we perfomed a gaussian fit process to the Halpha line on one of the obtained spectra and we obtain informations about the position of the peak of the line and its sigma (useful for the measurements of the dispersion velocity). We measured the value of the Halpha flux in order to measure the star formation rate of the galaxy.
- Cross matching the original list of 1300 sources with the catalogue of Tozzi et al (2006) A&A, 451, 457 'X-ray spectral properties of AGN in the Chandra Deep Field South': We loaded the Tozzi et al (2006) catalogue into TOPCAT using the Vizier catalogue Service option and then performed a cross match of this catalogue against our list of objects to search for known AGN.
