%0 Generic %1 ciocca2017colour %A Ciocca, Federica %A Saracco, Paolo %A Gargiulo, Adriana %A De Propris, Roberto %D 2017 %K color ellipticals grandient %R 10.1093/mnras/stx003 %T Colour gradients in cluster ellipticals at z~1.4: the hidden content of the galaxy central regions %U http://arxiv.org/abs/1701.02736 %X We present F775W-F850LP (rest-frame UV-U) and F850LP-F160W (rest-frame U-R) colour gradients for a sample of 17 elliptical galaxies morphologically selected in the cluster XMMU J2235.3-2557 at z=1.39. We detected significant negative (redder inwards) U-R colour gradients in ~70% of the galaxies and flat gradients for the remaining ones. On the other hand, the UV-U gradients are significant positive (bluer inwards) for ~80% of the galaxies and flat for the remaining ones. Using stellar population synthesis models, we found that the behaviour of the two colour gradients cannot be simultaneously explained by a radial variation of age, metallicity and/or dust. The observed U-R gradients are consistent with a metallicity gradient (mean value $\nabla_Z =-0.4$) in agreement with the one observed in the local elliptical galaxies. The positive UV-U gradients cannot be explained with age or metallicity variations and imply an excess of UV emission toward the galaxies' central regions. This excess calls into question mechanisms able to efficiently produce UV emission. The data require either steady weak star formation (<1 M$_ødot$ yr$^-1$) or a He-rich population in the cores of these galaxies in order to simultaneously reproduce both the colour gradients. On the contrary, the presence of a QSO cannot account for the observed UV excess on its own. We discuss these hypotheses on the basis of current observations and available models.

@misc{ciocca2017colour, abstract = {We present F775W-F850LP (rest-frame UV-U) and F850LP-F160W (rest-frame U-R) colour gradients for a sample of 17 elliptical galaxies morphologically selected in the cluster XMMU J2235.3-2557 at z=1.39. We detected significant negative (redder inwards) U-R colour gradients in ~70% of the galaxies and flat gradients for the remaining ones. On the other hand, the UV-U gradients are significant positive (bluer inwards) for ~80% of the galaxies and flat for the remaining ones. Using stellar population synthesis models, we found that the behaviour of the two colour gradients cannot be simultaneously explained by a radial variation of age, metallicity and/or dust. The observed U-R gradients are consistent with a metallicity gradient (mean value $\nabla_{Z} =-0.4$) in agreement with the one observed in the local elliptical galaxies. The positive UV-U gradients cannot be explained with age or metallicity variations and imply an excess of UV emission toward the galaxies' central regions. This excess calls into question mechanisms able to efficiently produce UV emission. The data require either steady weak star formation (<1 M$_\odot$ yr$^{-1}$) or a He-rich population in the cores of these galaxies in order to simultaneously reproduce both the colour gradients. On the contrary, the presence of a QSO cannot account for the observed UV excess on its own. We discuss these hypotheses on the basis of current observations and available models.}, added-at = {2017-01-12T10:26:57.000+0100}, author = {Ciocca, Federica and Saracco, Paolo and Gargiulo, Adriana and De Propris, Roberto}, biburl = {https://www.bibsonomy.org/bibtex/2252082bb80be78022c3e021c219d3ca0/miki}, description = {[1701.02736] Colour gradients in cluster ellipticals at z~1.4: the hidden content of the galaxy central regions}, doi = {10.1093/mnras/stx003}, interhash = {9896bdaab7cfcb744c51362b58fbfbeb}, intrahash = {252082bb80be78022c3e021c219d3ca0}, keywords = {color ellipticals grandient}, note = {cite arxiv:1701.02736Comment: 25 pages; 20 figures; accepted for publication in MNRAS}, timestamp = {2017-01-12T10:27:15.000+0100}, title = {Colour gradients in cluster ellipticals at z~1.4: the hidden content of the galaxy central regions}, url = {http://arxiv.org/abs/1701.02736}, year = 2017 }