Galaxy spectra

Spectra of the nucleus of NGC1068 from 3.2 - 3.7/on were obtained using CGS4 on the UKIRT on the nights of October 18 and 22 1991 (UT). The spectral resolution was 500 and the spatial resolution was 3.1 X 3.1 arcsec. Wavelength calibration was derived from three Xenon arc lines and is accurate to < 0.002 ou across the spectrum. The galaxy spectra were ratioed by a G5 star spectrum to remove atmospheric absorption. The two ni ts of data were merged and a continuum fitted to data outside the absorption feature was removed. 

The primordial Li abundance was sought primarily because of its ability to constrain the baryon to photon ratio in the Universe, or equivalently the baryon contribution to the critical density. In this way, Li was able to complement estimates from 4He, the primordial abundance of which varied only slightly with baryon density. Li also made up for the fact that the other primordial isotopes, 2H (i.e. D) and 3He, were at that time difficult to observe and/or interpret. During the late 1990 s, however, measurements of D in damped Lyman alpha systems (high column-density gas believed to be related to galaxy discs) provided more reliable constraints on the baryon density than Li could do (e.g. [19]). Even more recently, the baryon density has been inferred from the angular power spectrum of the cosmic microwave background radiation, for example from the WMAP measurements [26]. We consider the role of Li plateau observations post WMAP. 

The /1CDM paradigm for structure formation in the Universe, described in many hundreds of published papers, is very effective at reproducing observed large scale structure, based on a boundary condition of a scale-free Gaussian random power spectrum. Yet ACDM contains no information on the physics of whatever makes up CDM, and remains deficient in its description of galaxies and small-scale structures thus it is on galaxy scales and smaller where we can still learn the most, and hopefully attach some (astro-)physics to an ab initio power spectrum. 

Fig. 3.17. Spectrum of the central region of an SO galaxy, NGC 3384, showing hydrogen, magnesium and iron spectral features used in the Lick system. The resolution is 3.1 A ( 75kms 1), compared to a line-of-sight velocity dispersion 140kms 1. After Fisher, Franx and Illingworth (1996). Courtesy Garth Illingworth.

LINERs are weaker emission-line regions in certain elliptical and early-type spiral galaxies (e.g. M51 and M81) showing relatively strong lines of [O I], [N ii] and [S n], similar to SNR. It is not clear whether they are excited by shocks like SNR or by a very dilute (i.e. low u) non-thermal spectrum. 

Fig. 3.31. X-ray spectrum taken from the XMM-Newton and Chandra X-ray observatories of the inner part of the Centaurus cluster of galaxies, where the metallicity is roughly twice solar, showing the iron L- and K-shell features at energies of 1.2 and 6.8 keV repectively. The curve is a two-component fit to the continuum with temperatures of 0.7 and 1.5 keV. After Sanders and Fabian (2006). Courtesy Andy Fabian.

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).

Fig. 12.9. Composite spectrum of Lyman-break galaxies showing a combination of interstellar and stellar absorption lines, P Cygni features and nebular emission lines, dominated by Lyman-a. After Shapley et al. (2003).

Figure 15. A spectrum indicating the velocity of HCO+ molecules around the central black hole in the galaxy Centaurus A (NGC5128) [29]. Centaurus A is the nearest galaxy containing a supermassive black hole.

Many connections have been found between the luminosity peak, the shape of the light curve, evolution in the colour, spectral appearance, and membership of a galaxy of given morphology. However, after the first 150 days, uniformity takes over and all these objects fade in the same way and with the same spectrum. 

If SN1985f Was indeed 200 days old at the time of the observed spectrum, the model specfrum can he used to infer a distance to M83. This distance is 1 Mpc, Considered within the present uncertainties in the dis tance to this galaxy [13]. It is therefore worth noting that the model generates both a spectrum and a luminosity in reasonable agreement with observations in spite of the fact that it has only 0.6 M of O compared with the 5 M that has been previously claimed to be a requirement [16]. 

As far as we can see into the Universe, we don t observe any primordial antimatter. Within the limits of our present observational horizon the Universe is seen to contain only matter and no antimatter. The presence of cosmic antimatter would lead to observable traces of annihilation however the measurements of the extragalactic 7 ray flux indicate an absence of annihilation radiation, and the microwave background spectrum lacks a corresponding distortion. These findings preclude the existence of a significant amount of antimatter within tens of Megaparsecs, which is the scale of super-clusters of galaxies. 

The mass fluctuation spectrum gives rise to collapsed objects from galaxies to groups to rich clusters. The systems dominated by old stars - early type galaxies, elliptical-dominated groups, and rich clusters - all have gaseous halos... 

Figure 5.3. Left. The gamma-ray emission from XX annihilation in a rich, Coma-like, nearby galaxy cluster is shown Mx = 70 — 500 GeV (from top down). The integral flux is compared to the sensitivity of ongoing and planned gamma-ray experiments, as labelled. Right. The diffuse synchrotron emission spectrum of secondary electrons produced in XX annihilation is shown to fit the Coma radio-halo spectrum the green area represent the prediction of a model in which the x annihilates predominantly into fermions, while the blue area represent the gauge-boson dominated x annihilation (from Colafrancesco Mele 2001).

Several galaxy clusters show also an emission of extreme UV (Lieu et al. 1996, Durret et al. 2002) and soft X-ray (Bonamente et al. 2002, Kaastra et al. 2002) radiation in excess w.r.t. the thermal bremsstrahlung emission. This EUV emission excess may be consistent with both ICS of CMB photons off a non-thermal electron population (e.g., Lieu et al. 1999, Bowyer 2000) with Ee = 608.5 MeV (hv/keV)1/2 149 MeV for hv 60 eV, and with thermal emission from a warm gas at ksTe V 1 keV (Bonamente et al. 2002). In the case of Coma, the simple extrapolation of the ICS spectrum which fits the HXR excess down to energies 0.25 keV does not fit the EUV excess measured in Coma because it is too steep and yields a too high flux compared to the measured flux by the EUV satellite in the 0.065 — 0.245 keV band (Ensslin Biermann 1998). Thus, under the assumption that the HXR and the EUV emission of Coma is produced by ICS of CMB photons, the minimal requirement is that a break in the electron spectrum should be present in the range 0.3 — 2.8 GeV in order to avoid an excessive EUV contribution by the ICS emission and to be consistent with the radio halo spectrum. 

Figure 6.3. Left. The overall observed spectrum of the Coma cluster from radio to gamma-ray frequencies (see labels). Right. The constraints to the spectrum of relativistic electrons in Coma as obtained from different observation (see labels) the radio halo data (blue dashed lines) for different values of the IC magnetic field the HXR data (red solid fine with arrows), the EUV data (green solid line with arrows) and the EGRET upper limit (magenta arrow). The arrows indicate that the spectra should be considered as upper limits, because we cannot exclude that a fraction of the HXR and EUV flux is provided by active galaxies or warm gas, respectively.

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