ABSTRACT
The detailed modelling of the spectra observed from the long GRB031203 host galaxy at different epochs during the 2003–2009 yr is presented. The line profiles show FWHM of ∼100 $\rm km\, ...s^{-1}$. A broad-line profile with FWHM ≤ 400 $\rm km\, s^{-1}$ appears in the line sockets from the 2009 observations. We suggest that the narrow lines show the velocity of starburst (SB) debris, while the broad ones are due to the wind from SB stars. The spectra are emitted from the gas downstream of different shock fronts which are at work on the edges of the emitting clouds. A head-on-back shock appears when the wind from the SB stars reaches the internal edge of the SB debris moving outwards. A head-on shock is created by collision of the debris with the ISM clouds. Line ratios in both cases are calculated by the coupled effect of shock and photoionization from the SB. The models selected by fitting the calculated to the observed line ratios show that the ionization parameters, the shock velocities and the gas pre-shock densities slowly decrease with time. Oxygen metallicities (12+log(O/H) = 8.3–8.48) are lower than solar (8.82) by a factor <3 and nitrogen metallicities are lower than solar (12 + log(N/H) = 8.0, Grevesse & Sauval) by factors of 3–5.
Abstract
We revisit the line spectra emitted from long gamma-ray burst (LGRB) host galaxies at z ≤ 0.5 in order to calculate, through the detailed modelling of line ratios, the physical conditions ...and relative abundances in LGRB hosts in this redshift range. We have found lower metallicities than in LGRB hosts at higher z. New results regarding the metallicities and physical conditions in different regions throughout the LGRB 980425 host at z = 0.0085 are presented. In particular, we have found that the effective starburst temperature in the supernova (SN) region is the highest in the entire host galaxy. The low ionization parameter reveals that the radiation source is far away, or is somehow prevented from reaching the emitting gas in the SN region. Models constrained by a few oxygen, nitrogen and sulphur line ratios to Hβ in the LGRB 980425 host reproduce the He ii/Hβ and Ar iii/Hβ line ratios satisfactorily. Modelling of the observed S iv10.51 μm/S iii18.71 μm and Ne iii10.6 μm/Ne ii12.81 μm line ratios from the LGRB 031203 host galaxy at z = 0.105 shows that the mid-infrared lines are emitted from geometrically thin shock-dominated filaments that are not reached by photoionizing flux, while the optical lines are emitted from radiation-dominated outflowing clouds.
We present the spectral detailed modelling of NGC 4993 – the host galaxy of GW 170817 – and other short gamma-ray burst (SGRB) host galaxies. In order to determine their physical conditions and the ...element abundances, we have gathered spectroscopic and photometric data from the literature. The observation data are sometimes missing, preventing us from fully constraining the model. However, for most of the SGRB hosts the OIII5007/Hβ and NII6548/Hα line ratios are reported. The analysis of NGC 4993 by a composite model (photoionization+shock) confirms that an active galactic nucleus (AGN), most probably a low-ionization nuclear emission-line region (LINER) or a low-luminosity AGN (LLAGN) is the gas photoionization source. Shock velocities and preshock densities are similar to those found in the narrow line region of AGN. O/H and N/H have solar values. For the other SGRB of the sample, we found that O/H ratios are nearly solar, while N/H covers a much larger range of values at redshifts close to 0.4. In NGC 4993, the relative contribution to the spectral energy distribution of an old stellar population, characterized by a black-body temperature of Tbb = 4000 K, with respect to bremsstrahlung is higher by a factor of >100 than in most of the local AGN and starburst (SB) galaxies. For the other SGRB that compose the sample, Tbb ranges between 2000 K for SGRB 100206A and 8000 K for SGRB 111117A.
We explore the origin of the observed Lyα and other ultraviolet (UV) lines from galaxies at z < 3.7 by detailed modelling of their spectra. The objects are chosen from among those showing (a) ...UV–optical–near-IR lines, (b) only UV lines and (c) Lyα in the UV and a few optical lines. The total sample is heterogeneous, including galaxies in an all-sky radio survey, hard X-ray-emitting sources, a type 2 quasar (QSR)identified as a X-ray source, a type 2 active galactic nucleus (AGN) at high z (3.7), a very extended Lyα-emitting nebula, objects in a multi-band imaging survey for Lyman-break galaxies and in a slitless spectroscopic survey for Lyman-alpha emitters (LAEs), etc. We also present UV line predictions for a sample of galaxies in the 0.0686 < z < 0.8829 range. For calculation of the line and continuum spectra, we use the code suma, which accounts consistently for photoionizing flux from an external source and shocks. Dust-reprocessed radiation is also calculated. The results show that calculated Lyα/Hβ values are generally higher than observed, except for a few starburst (SB)-dominated models. Some spectra are better reproduced by shock-dominated models. The sample of galaxies including the Lyα line shows neither peculiar gas physical conditions nor abnormal element abundances. The line profiles have complex full widths at half maximum (FWHM) with two main components, which translate into two types of emitting gas clouds. High T
* values (>105 K), which indicate that SB stars are close to outburst, were found in a few objects. Traces of supernova events are suggested by a scandium emission line from the SST24 nebula and by shock-dominated models.
We present the detailed modelling of line spectra emitted from galaxies at redshifts 0.2≤ z ≤ 2.3. The spectra only account for a few oxygen to Hβ line ratios. The results show that OII3727+3729/Hβ ...and OIII5007+4959/Hβ are not sufficient to constrain the models. The data at least of an auroral line, e.g. OIII4363, should be known. We have found O/H relative abundances ranging between 1.8 ×10-4 and 6.6 × 10-4 by modelling the spectra observed from ultrastrong emission line galaxy and faint galaxy samples.
Using detailed modelling, we analyse the spectra observed from the sample galaxies at z ∼ 0.8 presented by Ly et al., constraining the models by the O iii5007+4959/O iii4363 line ratios. Composite ...models (shock + photoionization) are adopted. Shock velocities ≥100 km s−1 and pre-shock densities n
0 ∼ 200 cm−3 characterize the gas surrounding the starburst (SB), while n
0 are higher by a factor of 1.5–10 in the AGN emitting gas. SB effective temperatures are similar to those of quiescent galaxies (T
* ∼ 4–7 × 104 K). Cloud geometrical thicknesses in the SB are ≤1016 cm, indicating major fragmentation, while in AGN they reach >10 pc. O/H are about solar for all the objects, except for a few AGN clouds with O/H = 0.3–0.5 solar. SB models reproduce most of the data within the observational errors. About half of the objects’ spectra are well fitted by an accreting AGN. Some galaxies show multiple radiation sources, such as SB + AGN, or a double AGN.
We investigate “activity” and “quiescence” in galaxies at relatively high redshifts by modelling the line (and continuum) spectra of each object. The models account consistently for photoionization ...and shocks. We claim that the starburst effective temperature, the flux from an AGN, and the shock velocity are critical to activity. The results confirm that two sample galaxies show intense starburst activity with temperatures reaching T∗ = 2 × 105 K and shock velocities Vs> 250 km s-1, while for the remaining galaxies in our sample, the models show quiescent star formation with T∗ ≤ 7 × 104 K. A Seyfert 2-like AGN is proposed in one galaxy. The O/H relative abundances derived by the detailed modelling of the spectra are nearly solar for all the sample galaxies, in contrast to those obtained by direct methods.
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