Detection Of 21-cm Absorption Research Articles

Implications of a 21-cm signal for dark matter annihilation and decay

Measurements of the temperature of the baryons at the end of the cosmic dark ages can potentially set very precise constraints on energy injection from exotic sources, such as annihilation or decay of the dark matter. However, additional effects that lower the gas temperature can substantially weaken the expected constraints on exotic energy injection, whereas additional radiation backgrounds can conceal the effect of an increased gas temperature in measurements of the 21-cm hyperfine transition of neutral hydrogen. Motivated in part by recent claims of a detection of 21-cm absorption from a redshift of 17 by the EDGES experiment, we derive the constraints on dark matter annihilation and decay that can be placed in the presence of extra radiation backgrounds or effects that modify the gas temperature, such as dark matter-baryon scattering and early baryon-photon decoupling. We find that if the EDGES observation is confirmed, then constraints on light dark matter decaying or annihilating to electrons will in most scenarios be stronger than existing state-of-the-art limits from the cosmic microwave background, potentially by several orders of magnitude. More generally, our results allow mapping any future measurement of the global 21-cm signal into constraints on dark matter annihilation and decay, within the broad range of scenarios we consider.

The mid-infrared properties and gas content of active galaxies over large lookback times

Upon an expansion of all of the searches for redshifted HI 21-cm absorption (0.0021 < z 5.19), we update recent results regarding the detection of 21-cm in the non-local Universe. Specifically, we confirm that photo-ionisation of the gas is the mostly likely cause of the low detection rate at high redshift, in addition to finding that at z < 0.1 there may also be a decrease in the detection rate, which we suggest is due to the dilution of the absorption strength by 21-cm emission. By assuming that associated and intervening absorbers have similar cosmological mass densities, we find evidence that the spin temperature of the gas evolves with redshift, consistent with heating by ultra-violet photons. From the near--infrared (3.4, 4.6 and 12 micron) colours, we see that radio galaxies become more quasar-like in their activity with increasing redshift. We also find that the non-detection of 21-cm absorption at high redshift is not likely to be due to the selection of gas-poor ellipticals, in addition to a strong correlation between the ionising photon rate and the [3.4] - [4.6] colour, indicating that the UV photons arise from AGN activity. Like previous studies, we find a correlation between the detection of 21-cm absorption and the [4.6] - [12] colour, which is a tracer of star-forming activity. However, this only applies at the lowest redshifts (z < 0.1), the range considered by the other studies.

21-cm absorption from galaxies atz~ 0.3

We report the detection of 21-cm absorption from foreground galaxies towards quasars, specifically z_gal = 0.3120 towards SDSS J084957.97+510829.0 (z_qso = 0.584; Pair-I) and z_gal = 0.3714 towards SDSS J144304.53+021419.3 (z_qso = 1.82; Pair-II). In both the cases, the integrated 21-cm optical depth is consistent with the absorbing gas being a damped Lyman-\alpha (DLA) system. In the case of Pair-I, strong Na I and Ca II absorption are also detected at z_gal in the QSO spectrum. We identify an early-type galaxy at an impact parameter of b ~ 14 kpc whose photometric redshift is consistent with that of the detected metal and 21-cm absorption lines. This would be the first example of an early-type galaxy associated with an intervening 21-cm absorber. The gas detected in 21-cm and metal absorption lines in the outskirts of this luminous red galaxy could be associated with the reservoir of cold H I gas with a low level of star formation activity in the outer regions of the galaxy as reported in the literature for z ~ 0.1 early-type galaxies. In the case of Pair-II, the absorption is associated with a low surface brightness galaxy that, unlike most other known quasar-galaxy pairs (QGPs) i.e. QSO sight lines passing through disks/halos of foreground galaxies, is identified only via narrow optical emission lines detected on top of the QSO spectra. Using SDSS spectra we infer that the emission lines originate within ~ 5 kpc of the QSO sight line, and the gas has metallicity [12+O/H] ~ 8.4 and star formation rate ~ 0.7-0.8 M_sun per yr. The measured 21-cm optical depth can be reconciled with the N(H I) we derive from the measured extinction (A_V=0.6) if either the H I gas is warm or the extinction per hydrogen atom in this galaxy is much higher than the mean value of the Small Magellanic Cloud. (Abridged)

Localized HI 21-cm absorption towards a double-lobed z= 0.24 radio galaxy

Abstract We present the results of a mini-survey for associated HI 21-cm absorption at z≤ 0.42 with the Giant Metrewave Radio Telescope. Our targets are radio galaxies, selected on the basis that the γ ≈ 1216 Å luminosities are below LUV∼ 1023 W Hz-1, above which there has never been a detection of 21-cm absorption. Of the three sources for which we obtained good data, two are unclassified active galactic nuclei (AGNs) and one is type-2. Being a non-detection, the type-2 object is consistent with our previous result that 21-cm absorption in radio sources is not dictated by unified schemes of AGN. In the case of the detection, the absorption only occurs towards one of the two resolved radio lobes in PKS 1649-062. If the absorption is due to another intervening galaxy, or cool HI gas in the intergalactic medium, covering only the south-west (SW) lobe, then, being at the same redshift, this is likely to be gravitationally bound to the optical object identified as PKS 1649-062. If the absorption is due to an inclined disc centred between the lobes, intervening the SW lobe while being located behind the north-east (NE) lobe, by assuming that it covers the emission peak at ≈150 kpc from the nucleus, we estimate a dynamical mass of ≈3 × 1012 M⊙ for the disc.

Detection of the 2175 Å extinction feature and 21-cm absorption in two Mg ii systems at z ∼ 1.3

Abstract We have discovered two dusty intervening Mg ii absorption systems at z∼ 1.3 in the Sloan Digital Sky Survey (SDSS) data base. The overall spectra of both quasi-stellar objects (QSOs) are red (u−K &amp;gt; 4.5 mag) and are well modelled by the composite QSO spectrum reddened by the extinction curve from the Large Magellanic Cloud (LMC2) Supershell redshifted to the rest frame of the Mg ii systems. In particular, we detect clearly the presence of the ultraviolet (UV) extinction bump at λrest∼ 2175Å. Absorption lines of weak transitions like Si iiλ1808, Cr iiλ2056, Cr ii+ Zn iiλ2062, Mn iiλ2594, Ca iiλ3934 and Ti iiλ1910 from these systems are detected even in the low signal-to-noise ratio and low-esolution SDSS spectra, suggesting high column densities of these species. The depletion pattern inferred from these absorption lines is consistent with that seen in the cold neutral medium of the LMC. Using the LMC AV versus N(H i) relationship, we derive N(H i) ∼ 6 × 1021 cm−2 in both systems. Metallicities are close to solar. Giant Metrewave Radio Telescope (GMRT) observations of these two relatively weak radio QSOs (fν∼ 50 mJy) resulted in the detection of 21-cm absorption in both the cases. We show that the spin temperature of the gas is of the order of or smaller than 500 K. These systems provide a unique opportunity to search for molecules and diffuse interstellar bands at z &amp;gt; 1.

Detection of broad 21-cm absorption at zabs = 0.656 in the complex sight-line towards 3C 336

Abstract We report the detection of 21-cm absorption at zabs= 0.656 towards 1622 + 238 (3C336). The line is very broad with a full width to half-maximum of 235 km s−1, giving a velocity-integrated optical depth of . The centroid of the line is offset from that of the known damped Lyman α absorption system (DLA) by 50 km s−1, and if the Lyman α and 21-cm absorption are due to the same gas, we derive a spin temperature of Ts≤ 60 K, which would be the lowest yet in a DLA. The wide profile, which is over four times wider than that of any other DLA, supports the hypothesis that the hydrogen absorption is occurring either in the disc of a large underluminous spiral or in a group of dim unidentified galaxies, associated with the single object which has been optically identified at this redshift.

A new 21-cm absorber identified with an $L \sim L^\star$ galaxy

We present Giant Metrewave Radio Telescope (GMRT) observations of redshifted 21-cm absorption from the $z=0.437$ metal line absorption system towards PKS 1243-072. HI absorption is clearly detected; the absorption profile has a velocity spread of $\sim 20$ km/s. Detection of 21-cm absorption indicates that the absorber has an HI column density large enough to be classified as a damped Lyman-$\alpha$ system. Follow up ground based optical imaging and spectroscopy allow us to identify the absorber with an $L \sim L^\star$ galaxy at an impact parameter of $\sim 9.8$ kpc from the line of sight to the QSO. The absorbing galaxy is unusual in that it has bright emission lines. On the basis of the optical spectrum we are unable to uniquely classify the galaxy since its emission line ratios lie in the transition region between starburst and Seyfert II type spectra.

Detection of 21-cm absorption at Z of approximately 1.8 in the quasi-stellar object 1331+170

view Abstract Citations (83) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of 21-cm absorption at z ≈ 1.8 in the quasi-stellar object 1331+170. Wolfe, A. M. ; Davis, M. M. Abstract The detection of 21-cm absorption by neutral hydrogen in front of the QSO 1331+170 is reported. The line arises at 511.596 + or - 0.005 MHz, corresponding to a redshift, z=1.77642 + or - 0.00002, that is identical, within observational errors, to the previously detected optical redshift of absorption system A. The coincidence between radio and optical redshifts yields the strictest limit ever placed on the variation of certain physical constants over a look-back time comprising at least 65% of the current age of the universe, if the redshifts are cosmological. Comparison with a similar limit pertaining to the z=0.524 absorption event in AO 0235+164 indicates that physical constants in two globally separated regions also coincide. This is evidence for large-scale invariance of physical laws. An analysis of the L-alpha and 21-cm absorption data results in the determination of the spin temperature in a high-z object. If confirmed by future tests, the spin temperature of approximately 1000 K would imply a difference between H I in our Galaxy and in the absorber at z of approximately 1.8. Publication: The Astronomical Journal Pub Date: June 1979 DOI: 10.1086/112470 Bibcode: 1979AJ.....84..699W Keywords: Astronomical Spectroscopy; Electromagnetic Absorption; Neutral Gases; Quasars; Radio Astronomy; Absorption Spectra; Centimeter Waves; Hydrogen Clouds; Lyman Alpha Radiation; Red Shift; Spin Temperature; Astrophysics; Neutral Hydrogen:Quasars full text sources ADS | data products SIMBAD (4) NED (1)