arXiv subjects

J. M. Rodríguez Espinosa

Publications and source records attributed to J. M. Rodríguez Espinosa.

8 recordsLinked to original sources

arXiv2024

Discovery of a Lyα blob photo-ionised by a super-cluster of massive stars associated to a z = 3.49 galaxy

We report the discovery and characterisation of a Lya blob close to a galaxy at redshift z=3.49. We present our analysis to check whether the companion galaxy could be the source of the ionised photons responsible for the Lya emission from the blob. We use images obtained from the 10.4 m GTC telescope that are part of the SHARDS project. The blob is only visible in the F551W17 filter, centred around the Lya line at the redshift of the galaxy. We measure the luminosity of the blob with a two-step procedure. First, we describe the radial surface brightness (SB) profile of the galaxy using a Sersic function. We then remove this model from the SB profile of the blob and measure the luminosity of the blob alone. We also estimate the Lya continuum of the galaxy using an ACS image from the HST in the filter F606W, that is wider than the SHARDS one and centred at about the same wavelength. In this image the galaxy is visible, but the blob is not detected, since its Lya emission is diluted in the larger wavelength range of the F606W filter. We find that the Lya luminosity of the blob is 1.0x1043 erg s-1, in agreement with other Lya blobs reported in the literature. The luminosity of the galaxy in the same filter is 2.9x1042 erg s-1. The luminosity within the HST/ACS image is Lcont=1.1x1043 erg s-1. With these values we are able to estimate the Lya equivalent width (EW), that is found to be 111 Å (rest-frame). This value suggests that a super-cluster of massive (1-2x107 Msun) and young (2-4 Myr) stars could be responsible for the ionisation of the blob. We also use two other methods to estimate the luminosity of the galaxy and the blob, both supporting our conclusions. It is worth noting that the Lya blob is spatially decoupled from the galaxy by 5.7 kpc. This misalignment could suggest the presence of an ionised cone of escaping material, as found in nearby galaxies such as M82.

astro-ph.CO↗

arXiv2021

Probing the existence of a rich galaxy overdensity at z=5.2

We report the results of a pilot spectroscopic program of a region at z=5.2 in the GOODS-N field containing an overdensity of galaxies around the well-known submillimeter galaxy HDF850.1. We have selected candidate cluster members from the optical 25 medium-band photometric catalog of the project SHARDS (Survey for High-z Absorption Red and Dead Sources). 17 rest-frame UV selected galaxies (LAEs and LBGs) with 5.15 10^15 M_sun).

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arXiv2020

Differences and similarities of stellar populations in LAEs and LBGs at $z\sim$ 3.4 - 6.8

The differences between the inherent stellar populations (SPs) of LAEs and LBGs are a key factor in understanding early galaxy formation and evolution. We have run a set of SP burst-like models for a sample of 1,558 sources at $3.4<z<6.8$ from the Survey for High-$z$ Absorption Red and Dead Sources (SHARDS) over the GOODS-N field. This work focuses on the differences between the three different observational subfamilies of our sample: LAE-LBGs, no-Ly$α$ LBGs and pure LAEs. Single and double SP synthetic spectra were used to model the SEDs, adopting a Bayesian information criterion to analyse under which situations a second SP is required. We find that the sources are well modelled using a single SP in $\sim79\%$ of the cases. The best models suggest that pure LAEs are typically young low mass galaxies ($t\sim26^{+41}_{-25}$ Myr; $M_{\mathrm{star}}\sim5.6^{+12.0}_{-5.5}\times10^{8}\ M_{\odot}$), undergoing one of their first bursts of star formation. On the other hand, no-Ly$α$ LBGs require older SPs ($t\sim71\pm12$ Myr), and they are substantially more massive ($M_{\mathrm{star}}\sim3.5\pm1.1\times10^{9}\ M_{\odot}$). LAE-LBGs appear as the subgroup that more frequently needs the addition of a second SP, representing an old and massive galaxy caught in a strong recent star-forming episode. The relative number of sources found from each subfamily at each $z$ supports an evolutionary scenario from pure LAEs and single SP LAE-LBGs to more massive LBGs. Stellar Mass Functions are also derived, finding an increase of $M^{*}$ with cosmic time and a possible steepening of the low mass slope from $z\sim6$ to $z\sim5$ with no significant change to $z\sim4$. Additionally, we have derived the SFR-$M_{\mathrm{star}}$ relation, finding a $\mathrm{SFR}\propto M_{\mathrm{star}}^β$ behaviour with negligible evolution from $z\sim4$ to $z\sim6$.

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arXiv2018

A simultaneous search for High-$z$ LAEs and LBGs in the SHARDS survey

We have undertaken a comprehensive search for both Lyman Alpha Emitters (LAEs) and Lyman Break Galaxies (LBGs) in the SHARDS Survey of the GOODS-N field. SHARDS is a deep imaging survey, made with the 10.4 m Gran Telescopio Canarias (GTC), employing 25 medium band filters in the range from 500 to 941 nm. This is the first time that both LAEs and LBGs are surveyed simultaneously in a systematic way in a large field. We draw a sample of 1558 sources; 528 of them are LAEs. Most of the sources (1434) show rest-frame UV continua. A minority of them (124) are pure LAEs with virtually no continuum detected in SHARDS. We study these sources from $z\sim3.35$ up to $z\sim6.8$, well into the epoch of reionization. Note that surveys done with just one or two narrow band filters lack the possibility to spot the rest-frame UV continuum present in most of our LAEs. We derive redshifts, Star Formation Rates (SFRs), Ly$α$ Equivalent Widths (EWs) and Luminosity Functions (LFs). Grouping within our sample is also studied, finding 92 pairs or small groups of galaxies at the same redshift separated by less than 60 comoving kpc. In addition, we relate 87 and 55 UV-selected objects with two known overdensities at $z=4.05$ and $z=5.198$, respectively. Finally, we show that surveys made with broad band filters are prone to introduce many unwanted sources ($\sim20$% interlopers), which means that previous studies may be overestimating the calculated LFs, specially at the faint end.

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arXiv2017

GTC Observations of an Overdense Region of LAEs at z=6.5

We present the results of our search for the faint galaxies near the end of the Reionisation Epoch. This has been done using very deep OSIRIS images obtained at the Gran Telescopio Canarias (GTC). Our observations focus around two close, massive Lyman Alpha Emitters (LAEs) at redshift 6.5, discovered in the SXDS field within a large-scale overdense region (Ouchi et al. 2010). The total GTC observing time in three medium band filters (F883w35, F913w25 and F941w33) is over 34 hours covering $7.0\times8.5$ arcmin$^2$ (or $\sim30,000$ Mpc$^3$ at $z=6.5$). In addition to the two spectroscopically confirmed LAEs in the field, we have identified 45 other LAE candidates. The preliminary luminosity function derived from our observations, assuming a spectroscopic confirmation success rate of $\frac{2}{3}$ as in previous surveys, suggests this area is about 2 times denser than the general field galaxy population at $z=6.5$. If confirmed spectroscopically, our results will imply the discovery of one of the earliest protoclusters in the universe, which will evolve to resemble the most massive galaxy clusters today.

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arXiv2015

A deep look at the nuclear region of UGC 5101 through high angular resolution mid-IR data with GTC/CanariCam

We present an analysis of the nuclear infrared (IR, 1.6 to 18 $μ$m) emission of the ultraluminous IR galaxy UGC 5101 to derive the properties of its active galactic nucleus (AGN) and its obscuring material. We use new mid-IR high angular resolution ($0.3-0.5$ arcsec) imaging using the Si-2 filter ($λ_{C}=8.7\, μ$m) and $7.5-13$ $μ$m spectroscopy taken with CanariCam (CC) on the 10.4m Gran Telescopio CANARIAS. We also use archival HST/NICMOS and Subaru/COMICS imaging and Spitzer/IRS spectroscopy. We estimate the near- and mid-IR unresolved nuclear emission by modelling the imaging data with GALFIT. We decompose the Spitzer/IRS and CC spectra using a power-law component, which represents the emission due to dust heated by the AGN, and a starburst component, both affected by foreground extinction. We model the resulting unresolved near- and mid-IR, and the starburst subtracted CC spectrum with the CLUMPY torus models of Nenkova et al. The derived geometrical properties of the torus, including the large covering factor and the high foreground extinction needed to reproduce the deep $9.7\, μ$m silicate feature, are consistent with the lack of strong AGN signatures in the optical. We derive an AGN bolometric luminosity $L_{bol}\sim1.9\times10^{45}\,$erg s$^{-1}$ that is in good agreement with other estimates in the literature.

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arXiv2013

Nuclear star formation activity and black hole accretion in nearby Seyfert galaxies

Recent theoretical and observational works indicate the presence of a correlation between the star formation rate (SFR) and the active galactic nuclei (AGN) luminosity (and, therefore, the black hole accretion rate) of Seyfert galaxies. This suggests a physical connection between the gas forming stars on kpc scales and the gas on sub-pc scales that is feeding the black hole. We compiled the largest sample of Seyfert galaxies to date with high angular resolution (0.4-0.8 arcsec) mid-infrared (8-13 micron) spectroscopy. The sample includes 29 Seyfert galaxies drawn from the AGN Revised Shapley-Ames catalogue. At a median distance of 33 Mpc, our data allow us to probe nuclear regions on scales of 65 pc (median value). We found no general evidence of suppression of the 11.3 micron polycyclic aromatic hydrocarbon (PAH) emission in the vicinity of these AGN, and used this feature as a proxy for the SFR. We detected the 11.3 micron PAH feature in the nuclear spectra of 45% of our sample. The derived nuclear SFRs are, on average, five times lower than those measured in circumnuclear regions of 600 pc in size (median value). However, the projected nuclear SFR densities are a factor of 20 higher than those measured on circumnuclear scales. This indicates that the SF activity per unit area in the central 65 pc of Seyfert galaxies is much higher than at larger distances from their nuclei. We studied the connection between the nuclear SFR and the black hole accretion rate and showed that numerical simulations reproduce fairly well our observed relation.

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arXiv2006

The Narrow Line Region of the Seyfert 2 galaxy Mrk 78. An infrared view

We report near-infrared spectroscopic data for the Seyfert 2 galaxy Mrk 78, taken with the LIRIS near-infrared camera/spectrometer at the William Herschel Telescope (WHT). The long-slit spectra clearly show extended emission. The resolution and depth of the near-infrared spectra allows the examination of its morphology and ionization regions, and a direct comparison with similarly deep visible spectra. The emission-line ratios obtained are used to derive the extinction towards the nucleus. The detection of strong features such as [Fe II], H$_{2}$, hydrogen recombination lines and the coronal [Si VI]$λ$1.962 line is used to study the kinematics and excitation mechanisms occurring in Mrk 78, revealing that despite of the strong radio-jet interaction present in this object, photoionization from the active nucleus dominates the narrow line region emission, while UV fluorescence is the source of the H$_{2}$ emission. Lines with extended emission yield velocity distributions with an amplitude of about 600 km/s, the consequence of an eastern lobe moving away from us plus a western lobe with the opposite contribution. We used the photoionization code CLOUDY to recreate a typical narrow line region region, to derive the ionization parameter, and to compare our spectral data with diagnostic diagrams.

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