D. J. Saikia
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The organizations/institutes from the scholar's latest article
Previous Organizations / Institutes
The organizations / institutes from the scholar's other articles in the past ten years
Research Subjects
D. J. Saikia has a total of 116 co-authors. Here are the top co-authors by number of shared publications:
- Marek Jamrozy
Obserwatorium Astronomiczne, Uniwersytet Jagielloński
14 shared publications - Neeraj Gupta
Inter-University Centre for Astronomy and Astrophysics
12 shared publications - Judith A. Irwin
Department of Physics, Engineering Physics & Astronomy, Queen’s University
10 shared publications - C. H. Ishwara Chandra
National Centre For Radio Astrophysics, TIFR , Post bag 3, Ganeshkhind, Pune 411007
9 shared publications C. Konar
Inter-university Centre for Astronomy and Astrophysics Pune University Campus Post Bag 4 411 007 Pune India
9 shared publications- C. Konar
National Centre for Radio Astrophysics, TIFR, Pune University Campus, Post Bag 3, Pune 411 007, India
8 shared publications
Latest Publications
- 1 February 2018
- Published by Springer Nature in Resonance
- Vol. 23 (2) , 137-138
Editorial
- 1 February 2018
- Published by Springer Nature in Resonance
- Vol. 23 (2) , 147-163
Jets in Active Galaxies
- 1 February 2018
- Published by Springer Nature in Resonance
- Vol. 23 (2) , 147-163
Jets in Active Galaxies
- 1 February 2018
- Published by Springer Nature in Resonance
- Vol. 23 (2) , 235-239
Classics
- 17 April 2017
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 469 (3) , 3629-3640
H i, star formation and tidal dwarf candidate in the Arp 305 system
We present results from our Giant Metrewave Radio Telescope (GMRT) H i observations of the Arp 305 system. The system consists of two interacting spiral galaxies NGC 4016 and NGC 4017, a large amount of resultant tidal debris and a prominent tidal dwarf galaxy (TDG) candidate projected within the tidal bridge between the two principal galaxies. Our higher resolution GMRT H i mapping, compared to previous observations, allowed detailed study of smaller scale features. Our H i analysis supports the conclusion in Hancock et al. (2009) that the most recent encounter between the pair occurred ∼ 4 × 108 yrs ago. The GMRT observations also show H i features near NGC 4017 which may be remnants of an earlier encounter between the two galaxies. The H i properties of the Bridge TDG candidate blackinclude: MHI ∼ 6.6 × 108M⊙ and VHI = 3500± 7km s−1, which is in good agreement with the velocities of the parent galaxies. Additionally the TDG’s H i linewidth of 30 km s−1 and modest velocity gradient together with its SFR of 0.2 M⊙ yr−1 add to the evidence favouring the bridge candidate being a genuine TDG. The Bridge TDG’s Spitzer 3.6 μm and 4.5 μm counterparts with a [3.6]–[4.5] colour ∼ -0.2 mag suggests stellar debris may have seeded its formation. Future spectroscopic observations could confirm this formation scenario and provide the metallicity which is a key criteria for the validation for TDG candidates.
- 17 April 2017
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 469 (3) , 3629-3640
H i, star formation and tidal dwarf candidate in the Arp 305 system
We present results from our Giant Metrewave Radio Telescope (GMRT) H i observations of the Arp 305 system. The system consists of two interacting spiral galaxies NGC 4016 and NGC 4017, a large amount of resultant tidal debris and a prominent tidal dwarf galaxy (TDG) candidate projected within the tidal bridge between the two principal galaxies. Our higher resolution GMRT H i mapping, compared to previous observations, allowed detailed study of smaller scale features. Our H i analysis supports the conclusion in Hancock et al. (2009) that the most recent encounter between the pair occurred ∼ 4 × 108 yrs ago. The GMRT observations also show H i features near NGC 4017 which may be remnants of an earlier encounter between the two galaxies. The H i properties of the Bridge TDG candidate blackinclude: MHI ∼ 6.6 × 108M⊙ and VHI = 3500± 7km s−1, which is in good agreement with the velocities of the parent galaxies. Additionally the TDG’s H i linewidth of 30 km s−1 and modest velocity gradient together with its SFR of 0.2 M⊙ yr−1 add to the evidence favouring the bridge candidate being a genuine TDG. The Bridge TDG’s Spitzer 3.6 μm and 4.5 μm counterparts with a [3.6]–[4.5] colour ∼ -0.2 mag suggests stellar debris may have seeded its formation. Future spectroscopic observations could confirm this formation scenario and provide the metallicity which is a key criteria for the validation for TDG candidates.
- Open Access
HI, star formation and tidal dwarf candidate in the Arp 305 system
We present results from our Giant Metrewave Radio Telescope (GMRT) HI observations of the Arp 305 system. The system consists of two interacting spiral galaxies NGC 4016 and NGC 4017, a large amount of resultant tidal debris and a prominent tidal dwarf galaxy (TDG) candidate projected within the tidal bridge between the two principal galaxies. Our higher resolution GMRT HI mapping, compared to previous observations, allowed detailed study of smaller scale features. Our HI analysis supports the conclusion in Hancock et al. (2009) that the most recent encounter between the pair occurred $\sim$ 4 $\times$ 10$^8$ yrs ago. The GMRT observations also show HI features near NGC 4017 which may be remnants of an earlier encounter between the two galaxies. The HI properties of the Bridge TDG candidate include: M(HI) $\sim$ 6.6 $\times$ 10$^8$ msolar and V(HI) = 3500$\pm$ 7 km/s, which is in good agreement with the velocities of the parent galaxies. Additionally the TDG's HI linewidth of 30 km/s and a modest velocity gradient together with its SFR of 0.2 msolar/yr add to the evidence favouring the bridge candidate being a genuine TDG. The Bridge TDG's \textit{Spitzer} 3.6 $\mu$m and 4.5 $\mu$m counterparts with a [3.6]--[4.5] colour $\sim$ -0.2 mag suggests stellar debris may have seeded its formation. Future spectroscopic observations could confirm this formation scenario and provide the metallicity which is a key criteria for the validation for TDG candidates.Open AccessHI, star formation and tidal dwarf candidate in the Arp 305 system
We present results from our Giant Metrewave Radio Telescope (GMRT) HI observations of the Arp 305 system. The system consists of two interacting spiral galaxies NGC 4016 and NGC 4017, a large amount of resultant tidal debris and a prominent tidal dwarf galaxy (TDG) candidate projected within the tidal bridge between the two principal galaxies. Our higher resolution GMRT HI mapping, compared to previous observations, allowed detailed study of smaller scale features. Our HI analysis supports the conclusion in Hancock et al. (2009) that the most recent encounter between the pair occurred $\sim$ 4 $\times$ 10$^8$ yrs ago. The GMRT observations also show HI features near NGC 4017 which may be remnants of an earlier encounter between the two galaxies. The HI properties of the Bridge TDG candidate include: M(HI) $\sim$ 6.6 $\times$ 10$^8$ msolar and V(HI) = 3500$\pm$ 7 km/s, which is in good agreement with the velocities of the parent galaxies. Additionally the TDG's HI linewidth of 30 km/s and a modest velocity gradient together with its SFR of 0.2 msolar/yr add to the evidence favouring the bridge candidate being a genuine TDG. The Bridge TDG's \textit{Spitzer} 3.6 $\mu$m and 4.5 $\mu$m counterparts with a [3.6]--[4.5] colour $\sim$ -0.2 mag suggests stellar debris may have seeded its formation. Future spectroscopic observations could confirm this formation scenario and provide the metallicity which is a key criteria for the validation for TDG candidates. - Open Access
HI in the Arp 202 system and its tidal dwarf candidate
We present results from our Giant Metrewave Radio Telescope (GMRT) HI observations of the interacting pair Arp 202 (NGC 2719 and NGC 2719A). Earlier deep UV(GALEX) observations of this system revealed a tidal tail like extension with a diffuse object towards its end, proposed as a tidal dwarf galaxy (TDG) candidate. We detect HI emission from the Arp 202 system, including HI counterparts for the tidal tail and the TDG candidate. Our GMRT HI morphological and kinematic results clearly link the HI tidal tail and the HI TDG counterparts to the interaction between NGC 2719 and NGC 2719A, thus strengthening the case for the TDG. The Arp 202 TDG candidate belongs to a small group of TDG candidates with extremely blue colours. In order to gain a better understanding of this group we carried out a comparative study of their properties from the available data. We find that HI (and probably stellar) masses of this extremely blue group are similar to the lowest HI mass TDGs in the literature. However the number of such blue TDG candidates examined so far is too small to conclude whether or not their properties justify them to be considered as a subgroup of TDGs.
Open AccessHI in the Arp 202 system and its tidal dwarf candidate
We present results from our Giant Metrewave Radio Telescope (GMRT) HI observations of the interacting pair Arp 202 (NGC 2719 and NGC 2719A). Earlier deep UV(GALEX) observations of this system revealed a tidal tail like extension with a diffuse object towards its end, proposed as a tidal dwarf galaxy (TDG) candidate. We detect HI emission from the Arp 202 system, including HI counterparts for the tidal tail and the TDG candidate. Our GMRT HI morphological and kinematic results clearly link the HI tidal tail and the HI TDG counterparts to the interaction between NGC 2719 and NGC 2719A, thus strengthening the case for the TDG. The Arp 202 TDG candidate belongs to a small group of TDG candidates with extremely blue colours. In order to gain a better understanding of this group we carried out a comparative study of their properties from the available data. We find that HI (and probably stellar) masses of this extremely blue group are similar to the lowest HI mass TDGs in the literature. However the number of such blue TDG candidates examined so far is too small to conclude whether or not their properties justify them to be considered as a subgroup of TDGs.
- Open Access
- 2 July 2013
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 433 (4) , 2958-2974
The 617 MHz–λ 850 μm correlation (cosmic rays and cold dust) in NGC 3044 and NGC 4157
We present the first maps of NGC 3044 and NGC 4157 at λ 450 μm and λ 850 μm from the James Clerk Maxwell Telescope as well as the first maps at 617 MHz from the Giant Metrewave Radio Telescope. High-latitude emission has been detected in both the radio continuum and sub-mm for NGC 3044 and in the radio continuum for NGC 4157, including several new features. For NGC 3044, in addition, we find 617 MHz emission extending to the north of the major axis, beginning at the far ends of the major axis. One of these low-intensity features, more than 10 kpc from the major axis, has apparently associated emission at λ 20 cm and may be a result of in-disc activity related to star formation. The dust spectrum at long wavelengths required fitting with a two-temperature model for both galaxies, implying the presence of cold dust (Tc = 9.5 K for NGC 3044 and Tc = 15.3 K for NGC 4157). Dust masses are Md = 1.6 × 108 M⊙ and Md = 2.1 × 107 M⊙ for NGC 3044 and NGC 4157, respectively, and are dominated by the cold component. There is a clear correlation between the 617 MHz and λ 850 μm emission in the two galaxies. In the case of NGC 3044 for which the λ 850 μm data are strongly dominated by cold dust, this implies a relation between the non-thermal synchrotron emission and cold dust. The 617 MHz component represents an integration of massive star formation over the past 107–8 yr and the λ 850 μm emission represents heating from the diffuse interstellar radiation field (ISRF). The 617 MHz–λ 850 μm correlation improves when a smoothing kernel is applied to the λ 850 μm data to account for differences between the cosmic ray (CR) electron diffusion scale and the mean free path of an ISRF photon to dust. The best-fitting relation is $$L_{617_{\rm MHz}}\,\propto \,{L_{850\mu {\rm m}}}^{2.1\,\pm \,0.2}$$ for NGC 3044. If variations in the cold dust emissivity are dominated by variations in dust density, and the synchrotron emission depends on magnetic field strength (a function of gas density) as well as CR electron generation (a function of massive star formation rate and therefore density via the Schmidt law) then the expected correlation for NGC 3044 is $$L_{617_{\rm MHz}}\,\propto \,{L_{850\mu {\rm m}}}^{2.2}$$, in agreement with the observed correlation.- 2 July 2013
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 433 (4) , 2958-2974
Open AccessThe 617 MHz–λ 850 μm correlation (cosmic rays and cold dust) in NGC 3044 and NGC 4157
We present the first maps of NGC 3044 and NGC 4157 at λ 450 μm and λ 850 μm from the James Clerk Maxwell Telescope as well as the first maps at 617 MHz from the Giant Metrewave Radio Telescope. High-latitude emission has been detected in both the radio continuum and sub-mm for NGC 3044 and in the radio continuum for NGC 4157, including several new features. For NGC 3044, in addition, we find 617 MHz emission extending to the north of the major axis, beginning at the far ends of the major axis. One of these low-intensity features, more than 10 kpc from the major axis, has apparently associated emission at λ 20 cm and may be a result of in-disc activity related to star formation. The dust spectrum at long wavelengths required fitting with a two-temperature model for both galaxies, implying the presence of cold dust (Tc = 9.5 K for NGC 3044 and Tc = 15.3 K for NGC 4157). Dust masses are Md = 1.6 × 108 M⊙ and Md = 2.1 × 107 M⊙ for NGC 3044 and NGC 4157, respectively, and are dominated by the cold component. There is a clear correlation between the 617 MHz and λ 850 μm emission in the two galaxies. In the case of NGC 3044 for which the λ 850 μm data are strongly dominated by cold dust, this implies a relation between the non-thermal synchrotron emission and cold dust. The 617 MHz component represents an integration of massive star formation over the past 107–8 yr and the λ 850 μm emission represents heating from the diffuse interstellar radiation field (ISRF). The 617 MHz–λ 850 μm correlation improves when a smoothing kernel is applied to the λ 850 μm data to account for differences between the cosmic ray (CR) electron diffusion scale and the mean free path of an ISRF photon to dust. The best-fitting relation is $$L_{617_{\rm MHz}}\,\propto \,{L_{850\mu {\rm m}}}^{2.1\,\pm \,0.2}$$ for NGC 3044. If variations in the cold dust emissivity are dominated by variations in dust density, and the synchrotron emission depends on magnetic field strength (a function of gas density) as well as CR electron generation (a function of massive star formation rate and therefore density via the Schmidt law) then the expected correlation for NGC 3044 is $$L_{617_{\rm MHz}}\,\propto \,{L_{850\mu {\rm m}}}^{2.2}$$, in agreement with the observed correlation. - Open AccessThe 617 MHz - $λ$ 850 $μ$m Correlation (Cosmic Rays and Cold Dust) in NGC 3044 and NGC 4157We present the first maps of NGC 3044 and NGC 4157 at $\lambda\,450 \mu$m and $\lambda\,850 \mu$m from the JCMT as well as the first maps at 617 MHz from the GMRT. High latitude emission has been detected in both the radio continuum and sub-mm for NGC 3044 and in the radio continuum for NGC 4157, including several new features. The dust spectrum at long wavelengths required fitting with a two-temperature model for both galaxies, implying the presence of cold dust. Dust masses are $M_d\,=\,1.6\,\times\,10^8 M_\odot$ and $M_d\,=\,2.1\,\times\,10^7 M_\odot$ for NGC 3044 and NGC 4157, respectively, and are dominated by the cold component. There is a clear correlation between the 617 MHz and $\lambda\,850 \mu$m emission in the two galaxies. In the case of NGC 3044, this implies a relation between the non-thermal synchrotron emission and cold dust. The 617 MHz component represents an integration of massive star formation over the past $10^{7-8}$ yr and the $\lambda \,850 \mu$m emission represents heating from the diffuse interstellar radiation field (ISRF). The 617 MHz -- $\lambda\,850 \mu$m correlation improves when a smoothing kernel is applied to the $\lambda\,850 \mu$m data to account for differences between the CR electron diffusion scale and the mean free path of an ISRF photon to dust. The best-fit relation is $L_{617_{\rm MHz}}\,\propto\,{L_{850 \mu{\rm m}}}^{2.1\,\pm\,0.2}$ for NGC 3044. If variations in the cold dust emissivity are dominated by variations in dust density, and the synchrotron emission depends on magnetic field strength (a function of gas density) as well as CR electron generation (a function of massive star formation rate and therefore density via the Schmidt law) then the expected correlation for NGC 3044 is $L_{617_{\rm MHz}}\,\propto\,{L_{850 \mu{\rm m}}}^{2.2}$, in agreement with the observed correlation.Open AccessThe 617 MHz - $λ$ 850 $μ$m Correlation (Cosmic Rays and Cold Dust) in NGC 3044 and NGC 4157We present the first maps of NGC 3044 and NGC 4157 at $\lambda\,450 \mu$m and $\lambda\,850 \mu$m from the JCMT as well as the first maps at 617 MHz from the GMRT. High latitude emission has been detected in both the radio continuum and sub-mm for NGC 3044 and in the radio continuum for NGC 4157, including several new features. The dust spectrum at long wavelengths required fitting with a two-temperature model for both galaxies, implying the presence of cold dust. Dust masses are $M_d\,=\,1.6\,\times\,10^8 M_\odot$ and $M_d\,=\,2.1\,\times\,10^7 M_\odot$ for NGC 3044 and NGC 4157, respectively, and are dominated by the cold component. There is a clear correlation between the 617 MHz and $\lambda\,850 \mu$m emission in the two galaxies. In the case of NGC 3044, this implies a relation between the non-thermal synchrotron emission and cold dust. The 617 MHz component represents an integration of massive star formation over the past $10^{7-8}$ yr and the $\lambda \,850 \mu$m emission represents heating from the diffuse interstellar radiation field (ISRF). The 617 MHz -- $\lambda\,850 \mu$m correlation improves when a smoothing kernel is applied to the $\lambda\,850 \mu$m data to account for differences between the CR electron diffusion scale and the mean free path of an ISRF photon to dust. The best-fit relation is $L_{617_{\rm MHz}}\,\propto\,{L_{850 \mu{\rm m}}}^{2.1\,\pm\,0.2}$ for NGC 3044. If variations in the cold dust emissivity are dominated by variations in dust density, and the synchrotron emission depends on magnetic field strength (a function of gas density) as well as CR electron generation (a function of massive star formation rate and therefore density via the Schmidt law) then the expected correlation for NGC 3044 is $L_{617_{\rm MHz}}\,\propto\,{L_{850 \mu{\rm m}}}^{2.2}$, in agreement with the observed correlation.
- 21 December 2012
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 429 (3) , 2380-2391
Associated 21-cm absorption towards the cores of radio galaxies
- 21 December 2012
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 429 (3) , 2380-2391
Associated 21-cm absorption towards the cores of radio galaxies
- Open Access
Unusual displacement of HI due to tidal interaction in Arp 181
We present results from GMRT HI 21 cm line observations of the interacting galaxy pair Arp 181 (NGC 3212 and NGC 3215) at z =0.032. We find almost all of the detected HI (90%) displaced well beyond the optical disks of the pair with the highest density HI located ~70 kpc west of the pair. An HI bridge extending between the optical pair and the bulk of the HI together with their HI deficiencies provide strong evidence that the interaction between the pair has removed most of their HI to the current projected position. HI to the west of the pair has two approximately equal intensity peaks. The HI intensity maximum furthest to the west coincides with a small spiral companion SDSS J102726.32+794911.9 which shows enhanced mid-infrared (Spitzer), UV (GALEX) and H alpha emission indicating intense star forming activity. The HI intensity maximum close to the Arp 181 pair, coincides with a diffuse optical cloud detected in UV (GALEX) at the end of the stellar and HI tidal tails originating at NGC 3212 and, previously proposed to be a tidal dwarf galaxy in formation. Future sensitive HI surveys by telescopes like ASKAP should prove to be powerful tools for identifying tidal dwarfs at moderate to large redshifts to explore in detail the evolution of dwarf galaxies in the Universe.
Open AccessUnusual displacement of HI due to tidal interaction in Arp 181
We present results from GMRT HI 21 cm line observations of the interacting galaxy pair Arp 181 (NGC 3212 and NGC 3215) at z =0.032. We find almost all of the detected HI (90%) displaced well beyond the optical disks of the pair with the highest density HI located ~70 kpc west of the pair. An HI bridge extending between the optical pair and the bulk of the HI together with their HI deficiencies provide strong evidence that the interaction between the pair has removed most of their HI to the current projected position. HI to the west of the pair has two approximately equal intensity peaks. The HI intensity maximum furthest to the west coincides with a small spiral companion SDSS J102726.32+794911.9 which shows enhanced mid-infrared (Spitzer), UV (GALEX) and H alpha emission indicating intense star forming activity. The HI intensity maximum close to the Arp 181 pair, coincides with a diffuse optical cloud detected in UV (GALEX) at the end of the stellar and HI tidal tails originating at NGC 3212 and, previously proposed to be a tidal dwarf galaxy in formation. Future sensitive HI surveys by telescopes like ASKAP should prove to be powerful tools for identifying tidal dwarfs at moderate to large redshifts to explore in detail the evolution of dwarf galaxies in the Universe.