arXiv subjects

Ana Paulino-Afonso

Publications and source records attributed to Ana Paulino-Afonso.

28 records · Page 2Linked to original sources

arXiv2018

The clustering of typical Ly$α$ emitters from $z \sim 2.5 - 6$: host halo masses depend on Ly$α$ and UV luminosities

We investigate the clustering and halo properties of $\sim 5000$ Ly$α$-selected emission line galaxies (LAEs) from the Slicing COSMOS 4K (SC4K) and from archival NB497 imaging of SA22 split in 15 discrete redshift slices between $z \sim 2.5 - 6$. We measure clustering lengths of $r_0 \sim 3 - 6\ h^{-1}$ Mpc and typical halo masses of $\sim 10^{11}$ M$_\odot$ for our narrowband-selected LAEs with typical $L_{\rm{Ly}α} \sim 10^{42 - 43}$ erg s$^{-1}$. The intermediate band-selected LAEs are observed to have $r_0 \sim 3.5 - 15\ h^{-1}$ Mpc with typical halo masses of $\sim 10^{11 - 12}$ M$_\odot$ and typical $L_{\rm{Ly}α} \sim 10^{43 - 43.6}$ erg s$^{-1}$. We find a strong, redshift-independent correlation between halo mass and Ly$α$ luminosity normalized by the characteristic Ly$α$ luminosity, $L^\star(z)$. The faintest LAEs ($L \sim 0.1\ L^\star(z)$) typically identified by deep narrowband surveys are found in $10^{10}$ M$_\odot$ halos and the brightest LAEs ($L \sim 7\ L^\star(z)$) are found in $\sim 5 \times 10^{12}$ M$_\odot$ halos. A dependency on the rest-frame 1500 Å~UV luminosity, M$_\rm{UV}$, is also observed where the halo masses increase from $10^{11}$ to $10^{13}$ M$_\odot$ for M$_\rm{UV} \sim -19$ to $-23.5$ mag. Halo mass is also observed to increase from $10^{9.8}$ to $10^{12.3}$ M$_\odot$ for dust-corrected UV star formation rates from $\sim 0.6$ to $10$ M$_\odot$ yr$^{-1}$ and continues to increase up to $10^{13.5}$ M$_\odot$ in halo mass, where the majority of those sources are AGN. All the trends we observe are found to be redshift-independent. Our results reveal that LAEs are the likely progenitors of a wide range of galaxies depending on their luminosity, from dwarf-like, to Milky Way-type, to bright cluster galaxies. LAEs therefore provide unique insight into the early formation and evolution of the galaxies we observe in the local Universe.

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arXiv2018

Confirmation of double peaked Lyman-alpha emission at z=6.593: Witnessing a galaxy directly contributing to the reionisation of the Universe

Distant luminous Lyman-alpha emitters (LAEs) are excellent targets for spectroscopic observations of galaxies in the epoch of reionisation (EoR). We present deep high-resolution (R=5000) VLT/X-SHOOTER observations, along with an extensive collection of photometric data of `COLA1', a proposed double peaked LAE at z=6.6 (Hu et al. 2016). We rule out that COLA1's emission line is an [OII] doublet at z=1.475 on the basis of i) the asymmetric red line-profile and flux ratio of the peaks (blue/red=$0.31\pm0.03$) and ii) an unphysical [OII]/Ha ratio ([OII]/Ha > 22). We show that COLA1's observed B-band flux is explained by a faint extended foreground LAE, for which we detect Lya and [OIII] at z=2.142. We thus conclude that COLA1 is a real double-peaked LAE at z=6.593, the first discovered at z>6, confirming the result from Hu et al. (2016). COLA1 is UV luminous (M$_{1500}=-21.6\pm0.3$), has a high equivalent width (EW$_{0}$~120 Å) and very compact Lya emission (r$_{50} = 0.3$ kpc). Relatively weak inferred Hb+[OIII] line-emission from Spitzer/IRAC indicates an extremely low metallicity of Z<1/20 Z$_{\odot}$ or reduced strength of nebular lines due to high escape of ionising photons. The small Lya peak separation of $220\pm20$ km/s implies a low HI column density and an ionising photon escape fraction of ~15-30 %, providing the first direct evidence that such galaxies contribute actively to the reionisation of the Universe at z>6. Based on simple estimates, we find that COLA1 could have provided just enough photons to reionise its own ~0.3 pMpc bubble, allowing the blue Lya line to be observed. However, we also discuss alternative scenarios explaining the detected double peaked nature of COLA1. Our results show that future high-resolution observations of statistical samples of double peaked LAEs at z>5 are a promising probe of the occurrence of ionised regions around galaxies in the EoR.

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arXiv2018

VIS3COS: I. survey overview and the role of environment and stellar mass on star formation

We present the VIMOS Spectroscopic Survey of a Supercluster in the COSMOS field (VIS3COS) at z~0.84. We use VIMOS high-resolution spectra (GG475 filter) to spectroscopically select 490 galaxies in and around the super-structure and an additional 481 galaxies in the line of sight. We present the redshift distribution, the catalog to be made public and the first results on the properties of individual galaxies and stacked spectra (3500Å<λ<4200Å rest-frame). We probe a wide range of densities and environments (from low-density field to clusters and rich groups). We find a decrease in the median star formation rate from low to high density environments in all bins of stellar mass and a sharp rise of the quenched fraction (from ~10% to ~40-60%) of intermediate stellar mass galaxies $(10<\log_{10}\left(M_\star/\mathrm{M_\odot}\right)<10.75)$ from filaments to clusters. The quenched fraction for massive galaxies shows little dependence on the environment being constant at ~30-40%. We find a break in the strength of the [OII] emission, with nearly constant line equivalent widths at lower densities (~-11Å) and then a drop to ~-2.5Å towards higher densities. The break in the [OII] line strength happens at similar densities ($\log_{10}(1+δ)\sim0.0-0.5$) as the observed rise in the quenched fraction. Our results may provide further clues regarding the different environmental processes affecting galaxies with different stellar masses and highlight the advantages of a single dataset in the COSMOS field probing a wide range of stellar masses and environments. We hypothesize that quenching mechanisms are enhanced in high-density regions.

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arXiv2018

The nature of luminous Lyman-alpha emitters at z~2-3: maximal dust-poor starbursts and highly ionising AGN

Deep narrow-band surveys have revealed a large population of faint Lyman-alpha (Lya) emitters (LAEs) in the distant Universe, but relatively little is known about the most luminous sources ($L_{Lyα}>10^{42.7}$ erg/s; $L_{Lyα}>L^*_{Lyα}$). Here we present the spectroscopic follow-up of 21 luminous LAEs at z~2-3 found with panoramic narrow-band surveys over five independent extragalactic fields (~4x10$^6$ Mpc$^{3}$ surveyed at z~2.2 and z~3.1). We use WHT/ISIS, Keck/DEIMOS and VLT/X-SHOOTER to study these sources using high ionisation UV lines. Luminous LAEs at z~2-3 have blue UV slopes ($β=-2.0^{+0.3}_{-0.1}$), high Lya escape fractions ($50^{+20}_{-15}$%) and span five orders of magnitude in UV luminosity ($M_{UV}\approx-19$ to -24). Many (70%) show at least one high ionisation rest-frame UV line such as CIV, NV, CIII], HeII or OIII], typically blue-shifted by ~100-200 km/s relative to Lya. Their Lya profiles reveal a wide variety of shapes, including significant blue-shifted components and widths from 200 to 4000 km/s. Overall, 60+-11% appear to be AGN dominated, and at $L_{Lyα}>10^{43.3}$ erg/s and/or $M_{UV}<-21.5$ virtually all LAEs are AGN with high ionisation parameters (log U=0.6+-0.5) and with metallicities of ~0.5-1 Zsun. Those lacking signatures of AGN (40+-11%) have lower ionisation parameters ($\log U=-3.0^{+1.6}_{-0.9}$ and $\logξ_{\rm ion}=25.4\pm0.2$) and are apparently metal-poor sources likely powered by young, dust-poor "maximal" starbursts. Our results show that luminous LAEs at z~2-3 are a diverse population and that 2xL$^*_{Lyα}$ and 2xM$_{UV}^*$ mark a sharp transition in the nature of LAEs, from star formation dominated to AGN dominated.

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arXiv2018

On the UV compactness and morphologies of typical Lyman-a emitters from z~2 to z~6

We investigate the rest-frame UV morphologies of a large sample of Lyman-a emitters (LAEs) from z~2 to z~6, selected in a uniform way with 16 different narrow- and medium-bands over the full COSMOS field. We use 3045 LAEs with HST coverage in a stacking analysis and find that they have M_UV~-20, below M*_UV at these redshifts. We also focus our analysis on a subsample of 780 individual galaxies with i_AB<25 for which GALFIT converges for 429 of them. The individual median size (re~1 kpc), ellipticities (slightly elongated with (b/a)~0.45), Sérsic index (disk-like with n<2) and light concentration (comparable to that of disk or irregular galaxies, with C~2.7) of LAEs show mild evolution from z~2 to z~6. LAEs with the highest rest-frame equivalent widths (EW) are the smallest/most compact (re~0.8 kpc, compared to re~1.5 kpc for the lower EW LAEs). When stacking our samples in bins of fixed Lya luminosity and Lya EW we find evidence for redshift evolution in n and C, but not in galaxy sizes. The evolution seems to be stronger for LAEs with 25 5 to SFGs being a factor of ~2-4 larger than LAEs for z<2. This means that at the highest redshifts, where typical sizes approach those of LAEs, the fraction of galaxies showing Lya in emission (and with a high Lya escape fraction) should be much higher, consistent with observations.

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arXiv2018

Slicing COSMOS with SC4K: the evolution of typical Lya emitters and the Lya escape fraction from z~2 to z~6

We present and explore deep narrow- and medium-band data obtained with the Subaru and the Isaac Newton telescopes in the ~2 deg$^2$ COSMOS field. We use these data as an extremely wide, low-resolution (R~20-80) IFU survey to slice through the COSMOS field and obtain a large sample of ~4000 Lyman-$α$ (Lya) emitters from z~2 to z~6 in 16 redshift slices (SC4K). We present new Lya luminosity functions (LFs) covering a co-moving volume of ~10$^8$Mpc$^3$. SC4K extensively complements ultra-deep surveys, jointly covering over 4 dex in Lya luminosity and revealing a global (2.5 3.5, likely linked with the evolution of the AGN population. The Lya luminosity density rises by a factor ~2 from z~2 to z~3 but is then found to be roughly constant (~$1.1\times10^{40}$ erg s$^{-1}$ Mpc$^{-3}$) to z~6, despite the ~0.7 dex drop in UV luminosity density. The Lya/UV luminosity density ratio rises from $4\pm1$% to $30\pm6$% from z~2.2 to z~6. Our results imply a rise of a factor of ~2 in the global ionisation efficiency ($ξ_{\rm ion}$) and a factor ~$4\pm1$ in the Lya escape fraction from z~2 to z~6, hinting for evolution in both the typical burstiness/stellar populations and even more so in the typical ISM conditions allowing Ly$α$ photons to escape.

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arXiv2017

Spectroscopic properties of luminous Lyman-α emitters at $z \approx 6 - 7$ and comparison to the Lyman-break population

We present spectroscopic follow-up of candidate luminous Ly$α$ emitters (LAEs) at $z=5.7-6.6$ in the SA22 field with VLT/X-SHOOTER. We confirm two new luminous LAEs at $z=5.676$ (SR6) and $z=6.532$ (VR7), and also present {\it HST} follow-up of both sources. These sources have luminosities L$_{\rm Lyα} \approx 3\times10^{43}$ erg s$^{-1}$, very high rest-frame equivalent widths of EW$_0\gtrsim 200$ Å and narrow Ly$α$ lines (200-340 km s$^{-1}$). VR7 is the most UV-luminous LAE at $z>6.5$, with M$_{1500} = -22.5$, even brighter in the UV than CR7. Besides Ly$α$, we do not detect any other rest-frame UV lines in the spectra of SR6 and VR7, and argue that rest-frame UV lines are easier to observe in bright galaxies with low Ly$α$ equivalent widths. We confirm that Ly$α$ line-widths increase with Ly$α$ luminosity at $z=5.7$, while there are indications that Ly$α$ lines of faint LAEs become broader at $z=6.6$, potentially due to reionisation. We find a large spread of up to 3 dex in UV luminosity for $>L^{\star}$ LAEs, but find that the Ly$α$ luminosity of the brightest LAEs is strongly related to UV luminosity at $z=6.6$. Under basic assumptions, we find that several LAEs at $z\approx6-7$ have Ly$α$ escape fractions $\gtrsim100$ \%, indicating bursty star-formation histories, alternative Ly$α$ production mechanisms, or dust attenuating Ly$α$ emission differently than UV emission. Finally, we present a method to compute $ξ_{ion}$, the production efficiency of ionising photons, and find that LAEs at $z\approx6-7$ have high values of log$_{10}(ξ_{ion}$/Hz erg$^{-1}) \approx 25.51\pm0.09$ that may alleviate the need for high Lyman-Continuum escape fractions required for reionisation.

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arXiv2016

The CALYMHA survey: Lya luminosity function and global escape fraction of Lya photons at z=2.23

We present the CAlibrating LYMan-$α$ with H$α$ (CALYMHA) pilot survey and new results on Lyman-$α$ (Lya) selected galaxies at z~2. We use a custom-built Lya narrow-band filter at the Isaac Newton Telescope, designed to provide a matched volume coverage to the z=2.23 Ha HiZELS survey. Here we present the first results for the COSMOS and UDS fields. Our survey currently reaches a 3$σ$ line flux limit of ~4x10$^{-17}$ erg/s/cm$^{2}$, and a Lya luminosity limit of ~10$^{42.3}$ erg/s. We find 188 Lya emitters over 7.3x10$^5$ Mpc$^{3}$, but also find significant numbers of other line emitting sources corresponding to HeII, CIII] and CIV emission lines. These sources are important contaminants, and we carefully remove them, unlike most previous studies. We find that the Lya luminosity function at z=2.23 is very well described by a Schechter function up to L~10$^{43}$ erg/s with L$^*=10^{42.59+-0.05}$ erg/s, $ϕ^*=10^{-3.09+-0.08}$ Mpc$^{-3}$ and $α$=-1.75+-0.15. Above L~10$^{43}$ erg/s the Lya luminosity function becomes power-law like, driven by X-ray AGN. We find that Lya-selected emitters have a high escape fraction of 37+-7%, anti-correlated with Lya luminosity and correlated with Lya equivalent width. Lya emitters have ubiquitous large (~40 kpc) Lya haloes, 2x larger than their Ha extents. By directly comparing our Lya and Ha luminosity functions we find that the global/overall escape fraction of Lya photons (within a 13 kpc radius) from the full population of star-forming galaxies is 5.1+-0.2% at the peak of the star formation history. An extra 3.3+-0.3% of Lya photons likely still escape, but at larger radii.

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arXiv2016

The structural and size evolution of star-forming galaxies over the last 11 Gyrs

We present new results on the evolution of rest-frame blue/UV sizes and Sersic indices of H$α$-selected star-forming galaxies over the last 11 Gyrs. We investigate how the perceived evolution can be affected by a range of biases and systematics such as cosmological dimming and resolution effects. We use GALFIT and an artificial redshifting technique, which includes the luminosity evolution of H$α$-selected galaxies, to quantify the change on the measured structural parameters with redshift. We find typical sizes of 2 to 3 kpc and Sersic indices of n~1.2, close to pure exponential disks all the way from z=2.23 to z=0.4. At z=0 we find typical sizes of 4-5 kpc. Our results show that, when using GALFIT, cosmological dimming has a negligible impact on the derived effective radius for galaxies with <10 kpc, but we find a ~20% bias on the estimate of the median Sersic indices, rendering galaxies more disk-like. Star-forming galaxies have grown on average by a factor of 2-3 in the last 11 Gyrs with $r_e\propto(1+z)^{-0.75}$. By exploring the evolution of the stellar mass-size relation we find evidence for a stronger size evolution of the most massive star-forming galaxies since z~2, as they grow faster towards z~0 when compared to the lower stellar mass counterparts. As we are tracing the rest-frame blue/UV, we are likely witnessing the growth of disks where star formation is ongoing in galaxies while their profiles remain close to exponential disks, n<1.5, across the same period.

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arXiv2016

The CALYMHA survey: Ly$α$ escape fraction and its dependence on galaxy properties at $z=2.23$

We present the first results from our CAlibrating LYMan-$α$ with H$α$ (CALYMHA) pilot survey at the Isaac Newton Telescope. We measure Ly$α$ emission for 488 H$α$ selected galaxies at $z=2.23$ from HiZELS in the COSMOS and UDS fields with a specially designed narrow-band filter ($λ_c$ = 3918 Å, $Δλ$= 52 Å). We find 17 dual H$α$-Ly$α$ emitters ($f_{\rm Lyα} >5\times10^{-17}$ erg s$^{-1}$ cm$^{-2}$, of which 5 are X-ray AGN). For star-forming galaxies, we find a range of Ly$α$ escape fractions (f$_{\rm esc}$, measured with 3$"$ apertures) from $2$\%$-30$\%. These galaxies have masses from $3\times10^8$ M$_{\odot}$ to 10$^{11}$ M$_{\odot}$ and dust attenuations E$(B-V)=0-0.5$. Using stacking, we measure a median escape fraction of $1.6\pm0.5$\% ($4.0\pm1.0$\% without correcting H$α$ for dust), but show that this depends on galaxy properties. The stacked f$_{\rm esc}$ tends to decrease with increasing SFR and dust attenuation. However, at the highest masses and dust attenuations, we detect individual galaxies with f$_{\rm esc}$ much higher than the typical values from stacking, indicating significant scatter in the values of f$_{\rm esc}$. Relations between f$_{\rm esc}$ and UV slope are bimodal, with high f$_{\rm esc}$ for either the bluest or reddest galaxies. We speculate that this bimodality and large scatter in the values of f$_{\rm esc}$ is due to additional physical mechanisms such as outflows facilitating f$_{\rm esc}$ for dusty/massive systems. Ly$α$ is significantly more extended than H$α$ and the UV. f$_{\rm esc}$ continues to increase up to at least 20 kpc (3$σ$, 40 kpc [2$σ$]) for typical SFGs and thus the aperture is the most important predictor of f$_{\rm esc}$.

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