ABSTRACT
We here report the detection of extended He ii λ4686 nebular emission in the central region of NGC 1569 using the integral field spectrograph MEGARA at the 10.4 m Gran Telescopio Canarias. ...The observations cover a field of view (FoV) of 12.5 arcsec × 11.3 arcsec at a seeing-limited spatial resolution of ∼15 pc and at a spectral resolution of R = 6000 in the wavelength range 4330–5200 Å. The emission extends over a semicircular arc of ∼40 pc width and ∼150 pc diameter around the superstar cluster A (SSC-A). The AV derived using Balmer decrement varies from the Galactic value of 1.6 mag to a maximum of ∼4.5 mag, with a mean value of 2.65 ± 0.60 mag. We infer 124 ± 11 Wolf–Rayet (WR) stars in SSC-A using the He ii λ4686 broad feature and AV = 2.3 mag. The He+ ionizing photon rate from these WR stars is sufficient to explain the luminosity of the He ii nebula. The observationally determined total He+ and H0 ionizing photon rates, their ratio, and the observed number of WR stars in SSC-A are all consistent with the predictions of simple stellar population models at an age of 4.0 ± 0.5 Myr and a mass of (5.5 ± 0.5) × 105 M⊙. Our observations reinforce the absence of WR stars in SSC-B, the second most massive cluster in the FoV. None of the other locations in our FoV where He ii λ4686 emission has been reported from narrow-band imaging observations contain WR stars.
We explore the possibility of setting stringent constraints to the dark energy equation of state using alternative cosmic tracers like (a) the Hubble relation using H ii galaxies, which can be ...observed at much higher redshifts (z≲ 3.5) than those currently traced by Type Ia supernovae (SNeIa) samples, and (b) the large-scale structure using the clustering of X-ray selected active galactic nuclei (AGN), which have a redshift distribution peaking at z∼ 1.
In this paper we use extensive Monte Carlo simulations to define the optimal strategy for the recovery of the dark energy equation of state using the high-redshift (z≳ 2) Hubble relation, but accounting also for the effects of gravitational lensing, which for such high redshifts can significantly affect the derived cosmological constraints. We investigate the size of the sample of high-z H ii galaxies needed to provide useful constraints in the dark energy equation of state. Based on a 'figure of merit' analysis, we provide estimates for the number of 2 ≲z≲ 3.5 tracers needed to reduce the cosmological solution space, presently provided by the Constitution SNIa set, by a desired factor. The analysis is given for any level of rms distance modulus uncertainty and we find that an expected reduction (i.e. by ∼20-40 per cent) of the current level of H ii-galaxy-based distance modulus uncertainty does not provide a significant improvement in the derived cosmological constraints. It is much more efficient to increase the number of tracers than to reduce their individual uncertainties.
Finally, we propose a framework to put constraints on the dark energy equation of state by using the joint likelihood of the X-ray AGN clustering and of the Hubble relation cosmological analyses. A preliminary joint analysis using the X-ray AGN clustering of the 2XMM survey and the Hubble relation of the Constitution SNIa set provide Ωm= 0.31 ± 0.01 and w=−1.06 ± 0.05. We also find that the joint SNIa-2XMM analysis provides significantly more stringent cosmological constraints, increasing the figure of merit by a factor of ∼2, with respect to that of the joint SNIa-baryonic acoustic oscillation analysis.
Extragalactic very-high-energy (VHE; E > 100 GeV) sources are unique objects to study the most powerful particle accelerators in nature, as active galactic nuclei are likely sources of ...ultra-high-energy cosmic rays. BL Lacertae blazars are the most frequent extragalactic objects found in the VHE gamma-ray catalogs. It is very difficult to estimate their redshifts, considering they have no strong enough optical spectral features, hence ∼20% of them have unknown or poorly constrained redshifts. KUV 00311-1938 is a VHE BL Lacertae blazar, with an uncertain redshift in the range of 0.5 < z < 0.98. We have obtained deep spectroscopy using Gemini and the GTC telescopes of KUV 00311-1938 and its surroundings with high signal-to-noise ratio in 2016-2017. The lack of features did not allow us to determine the spectroscopic redshift of KUV 00311-1938; nevertheless, we obtain a lower limit of z 0.475. We determined the redshifts of 41 galaxies observed in the field-of-view of the blazar and through a population study, identified three pairs and four groups consisting of 3 or 4 members with redshifts in the range z = 0.1468-0.4756. Due to the absence of a large group of galaxies, we could not associate KUV 00311-1938 with any of the groups detected.
We have derived ages, metallicities and enhanced-element ratios α/Fe for a sample of 83 early-type galaxies essentially in groups, the field or isolated objects. The stellar-population properties ...derived for each galaxy correspond to the nuclear re/8 aperture extraction. The median age found for Es is 5.8±0.6 Gyr and the average metallicity is +0.37±0.03 dex. For S0s, the median age is 3.0±0.6 Gyr and Z/H= 0.53±0.04 dex. We compare the distribution of our galaxies in the Hβ-MgFe diagram with Fornax galaxies. Our elliptical galaxies are 3–4 Gyr younger than Es in the Fornax cluster. We find that the galaxies lie in a plane defined by Z/H= 0.99 log σ0− 0.46 log(age) − 1.60, or in linear terms Z ∝σ0× (age) −0.5. More massive (larger σ0) and older galaxies present, on average, large α/Fe values, and therefore must have undergone shorter star-formation time-scales. Comparing group against field/isolated galaxies, it is not clear that environment plays an important role in determining their stellar-population history. In particular, our isolated galaxies show ages differing by more than 8 Gyr. Finally we explore our large spectral coverage to derive log (O/H) metallicity from the Hα and N iiλ6584 and compare it with model-dependent Z/H. We find that the O/H abundances are similar for all galaxies, and we can interpret it as if most chemical evolution has already finished in these galaxies.
Emission-line properties of Seyfert 2 nuclei Gu, Q.; Melnick, J.; Fernandes, R. Cid ...
Monthly Notices of the Royal Astronomical Society,
February 2006, Letnik:
366, Številka:
2
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
This is the third paper of a series devoted to the study of the global properties of Joguet's sample of 79 nearby galaxies observable from the southern hemisphere, of which 65 are Seyfert 2 ...galaxies. We use the population synthesis models of Paper II to derive ‘pure’ emission‐line spectra for the Seyfert 2 galaxies in the sample, and thus explore the statistical properties of the nuclear nebular components and their relation to the stellar populations. We find that the emission‐line clouds suffer substantially more extinction than the starlight, and we confirm the correlations between stellar and nebular velocity dispersions and between emission‐line luminosity and velocity dispersions, although with substantial scatter. Nuclear luminosities correlate with stellar velocity dispersions, but Seyferts with conspicuous star‐forming activity deviate systematically towards higher luminosities. Removing the contribution of young stars to the optical continuum produces a tighter and steeper relation, L∝σ4★, consistent with the Faber–Jackson law.
Emission‐line ratios indicative of the gas excitation such as O iii/Hβ and O iii/O ii are statistically smaller for Seyferts with significant star formation, implying that ionization by massive stars is responsible for a substantial and sometimes even a dominant fraction of the Hβ and O ii fluxes. We use our models to constrain the maximum fraction of the ionizing power that can be generated by a hidden active galactic nucleus (AGN). We correlate this fraction with classical indicators of AGN photoionization (i.e. X‐ray luminosity and nebular excitation), but find no significant correlations. Thus, while there is a strong contribution of starbursts to the excitation of the nuclear nebular emission in low‐luminosity Seyferts, the contribution of the hidden AGN remains elusive even in hard X‐rays.
We propose a methodology to perform a self-consistent analysis of the physical properties of the emitting gas of H ii galaxies adequate to the data that can be obtained with the 21st century ...technology. This methodology requires the production and calibration of empirical relations between the different line temperatures that should supersede currently used ones based on very simple, and poorly tested, photoionization model sequences. As a first step to reach these goals, we have obtained simultaneous blue to far red long-slit spectra with the William Herschel Telescope (WHT) of three compact H ii galaxies selected from the Sloan Digital Sky Survey (SDSS) Data Release 2 (DR2) spectral catalogue using the INAOE Virtual Observatory superserver. Our spectra cover the range from 3200 to 10 500 Å, including the Balmer jump, the O ii λλ 3727, 29 Å lines, the S iii λλ 9069, 9532 Å doublet as well as various weak auroral lines such as O iii λ 4363 Å and S iii λ 6312 Å. For the three objects, we have measured at least four line temperatures, T(O iii), T(S iii), T(O ii) and T(S ii), and the Balmer continuum temperature T(Bac). These measurements and a careful and realistic treatment of the observational errors yield total oxygen abundances with accuracies between 5 and 9 per cent. These accuracies are expected to improve as better calibrations based on more precise measurements, both on electron temperatures and densities, are produced. We have compared our obtained spectra with those downloaded from the SDSS DR3 finding a satisfactory agreement. The analysis of these spectra yields values of line temperatures and elemental ionic and total abundances which are in general agreement with those derived from the WHT spectra, although for most quantities they can only be taken as estimates since, due to the lack of direct measurements of the required lines, theoretical models had to be used whose uncertainties are impossible to quantify. The ionization structure found for the observed objects from the O+/O2+ and S+/S2+ ratios points to high values of the ionizing radiation, as traced by the values of the ‘softness parameter’η which is less than 1 for the three objects. The use of line temperatures derived from T(O iii) based on current photoionization models yields for the two highest excitation objects, much higher values of η which would imply lower ionizing temperatures. This is, however, inconsistent with the ionization structure as probed by the measured emission-line intensities. Finally, we have measured the T(Bac) for the three observed objects and derived temperature fluctuations. Only for one of the objects, the temperature fluctuation is significant and could lead to higher oxygen abundances by about 0.20 dex.
Abstract
We report on the redshift of the BL Lac object 3FGL J0909.0+2310 based on observations obtained with the OSIRIS Multi-Object Spectrograph (MOS) mounted on the 10.4-m Gran Telescopio ...Canarias. A redshift of 0.432 ± 0.002 was obtained by the identification of three absorption features (Ca ii K&H and the G band) detected in the spectrum of the BL Lac host galaxy. The closest object to the BL Lac at an angular separation of 3.8 arcsec (∼21 kpc at this distance) has a similar redshift of 0.431 ± 0.002. This companion galaxy could be the most likely cause of the nuclear activity as postulated by studies based on more extended data sets and cosmological models. MOS allows us to study the object's neighbourhood within a field of view of approximately 7 × 2 arcmin2 and we find two small groups of galaxies at redshifts 0.28 and 0.39 which are probably not related to the activity of 3FGL J0909.0+2310.
We demonstrate that the evolution of the QSO luminosity density with epoch displays a striking similarity to the cosmological evolution of the field galaxy star formation rate, recently derived from ...a number of independent surveys. The QSO luminosity density at 2800 Å is approximately one-fortieth that implied by the star formation rate in galaxies throughout the past 11 Gyr (z > 4). This similarity suggests that a substantial fraction of the QSO luminosity may be closely linked to the star formation process and its evolution with cosmic time.
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