Galaxies redshift

Spergel et al. 2007), but greatly exceeds the smoothed-out cosmological density of luminous matter deduced from galaxy redshift surveys, which give a luminosity density in blue light... 

When the light is dominated by massive stars, e.g. in starburst galaxies, the luminosity is related in turn to the rate of metal production, since virtually all processed material is ejected in the form of metals (and some helium). Thus there is a relationship between the total co-moving luminosity density, the monochromatic luminosity density (deduced from star-forming galaxy redshift surveys with appropriate corrections for absorption) in a fixed frequency bandwidth (anywhere between 912 and about 2000 A in the rest frame) and the mass going into nucleosynthesis ... 

The main limitation of the previous method is the time needed to detect (and to treat) optical spectroscopic data. A possible solution to this problem is to use photometric redshifts. Using five bands observed in photometry only (for example from the B to the J band) allows robust galaxy redshift determinations... 

It is also interesting to note that solar metallicities are reported for z=2, e.g. [22], and that disks of old stars have been found at redshifts as high as z=2.5, see e.g. [23]. These types of findings indicate that indeed the formation of the thick disk in our galaxy might have happened well in the past. 

In the next very few years stellar abundances and kinematics will be available for as many stars as redshifts are now available for galaxies. This abundance of information can, provided we approach the analysis and interpretation with due imagination, advance the astrophysics of galaxy formation as much as Cosmology has advanced over the last few decades. No doubt our image of galaxy evolution will be similarly revolutionised. 

The epoch and mode of galaxy formation are not well known, but both quasars and star-forming galaxies are known with redshifts up to about 7, corresponding to an era when the expanding Universe was only 1/8 of its present size, and the emission-line spectra of quasars indicate a large heavy-element abundance (solar or more Hamann Ferland 1999), suggesting prior stellar activity. The first stars, on the other hand, known as Population IIP, would have been devoid of metals whether they differed from normal stars in other basic characteristics, notably their mass distribution, is not known, since no completely metal-free stars have been... 

Fig. 4.10. Portion of the red spectrum of the H II galaxy Tololo 0633-415 with a redshift of 0.016, showing diagnostic features for helium (Ha and X 6678), electron density ([S n]) and ionization ([S hi]). The features marked cosmic ray are due to impacts of charged particles on the CCD detector. After Pagel et al. (1992).

Observations of distant objects, notably high-redshift star-forming ( Lyman-break ) galaxies and absorption line systems on the line of sight to quasars, give some information on chemical evolution at epochs not too far from when the first stars and most galaxies were presumably formed. Other information comes from two related effects ... 

The IRAS satellite mission, launched in 1983, provided a more complete survey of disk and active galaxies containing dust than had been possible from optical observations. Follow-up measurements of redshifts and other properties led to significant results for cosmology and the discovery of many luminous star-forming and active galaxies enshrouded by dust. A typical spiral galaxy like our own... 

The IRAS galaxies provided some of the earliest evidence from redshift surveys, and from source counts as a function of observed flux, that the spiral galaxy population has undergone evolution (ORS see Fig. 12.2). This result is analogous to similar evidence from source counts of radio galaxies and quasars, as well as quasar redshifts, and a correlation that has been observed between radio and infrared luminosity suggests that the evolution could be similar in both cases. Typical simple models for such evolution include luminosity evolution according to... 

Fig. 12.6. Observable baryons in the Universe as a function of time. The curves represent the total mass density in stars (in Af0Mpc-3) from Rudnick et al. (2003) based on a survey of near-infrared selected galaxies in the Hubble Deep Field South, assuming a Salpeter(O.l) IMF. (For a Kennicutt (1983) IMF, the numbers would be approximately halved.) The points with error bars show the cosmic density of H I from DLAs and sub-DLAs at various redshifts, uncorrected for obscuration, while the point at bottom right shows the present-day density of H i clouds determined by Zwaan et al. (2005). The typical H I co-moving volume density corresponds to S2Hi — 0.7 x 10-3 (taking h = 0.65). After Peroux, Dessauges-Zavatsky, D Odorico et al. (2005).

Sub-mm galaxies are another class of star-forming galaxies at typical redshifts around 2 found using the SCUBA detector5 and pin-pointed from their radio... 

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